diff --git a/buildSrc/src/main/java/org/springframework/boot/build/architecture/ArchitectureCheck.java b/buildSrc/src/main/java/org/springframework/boot/build/architecture/ArchitectureCheck.java
index ed1cb29a69e..a3c545cef87 100644
--- a/buildSrc/src/main/java/org/springframework/boot/build/architecture/ArchitectureCheck.java
+++ b/buildSrc/src/main/java/org/springframework/boot/build/architecture/ArchitectureCheck.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2022-2024 the original author or authors.
+ * Copyright 2012-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -81,7 +81,8 @@ public abstract class ArchitectureCheck extends DefaultTask {
 				allBeanFactoryPostProcessorBeanMethodsShouldBeStaticAndHaveNoParameters(),
 				noClassesShouldCallStepVerifierStepVerifyComplete(),
 				noClassesShouldConfigureDefaultStepVerifierTimeout(), noClassesShouldCallCollectorsToList(),
-				noClassesShouldCallURLEncoderWithStringEncoding(), noClassesShouldCallURLDecoderWithStringEncoding());
+				noClassesShouldCallURLEncoderWithStringEncoding(), noClassesShouldCallURLDecoderWithStringEncoding(),
+				noClassesShouldCallStringToUpperCaseWithoutLocale(), noClassesShouldCallStringToLowerCaseWithoutLocale());
 		getRules().addAll(getProhibitObjectsRequireNonNull()
 			.map((prohibit) -> prohibit ? noClassesShouldCallObjectsRequireNonNull() : Collections.emptyList()));
 		getRuleDescriptions().set(getRules().map((rules) -> rules.stream().map(ArchRule::getDescription).toList()));
@@ -181,6 +182,20 @@ public abstract class ArchitectureCheck extends DefaultTask {
 		};
 	}
 
+	private ArchRule noClassesShouldCallStringToLowerCaseWithoutLocale() {
+		return ArchRuleDefinition.noClasses()
+			.should()
+			.callMethod(String.class, "toLowerCase")
+			.because("String.toLowerCase(Locale.ROOT) should be used instead");
+	}
+
+	private ArchRule noClassesShouldCallStringToUpperCaseWithoutLocale() {
+		return ArchRuleDefinition.noClasses()
+			.should()
+			.callMethod(String.class, "toUpperCase")
+			.because("String.toUpperCase(Locale.ROOT) should be used instead");
+	}
+
 	private ArchRule noClassesShouldCallStepVerifierStepVerifyComplete() {
 		return ArchRuleDefinition.noClasses()
 			.should()
diff --git a/buildSrc/src/test/java/org/springframework/boot/build/architecture/ArchitectureCheckTests.java b/buildSrc/src/test/java/org/springframework/boot/build/architecture/ArchitectureCheckTests.java
index 598d8d2fbe2..fc76dbd488f 100644
--- a/buildSrc/src/test/java/org/springframework/boot/build/architecture/ArchitectureCheckTests.java
+++ b/buildSrc/src/test/java/org/springframework/boot/build/architecture/ArchitectureCheckTests.java
@@ -146,6 +146,42 @@ class ArchitectureCheckTests {
 		});
 	}
 
+	@Test
+	void whenClassCallsStringToUpperCaseWithoutLocaleFailsAndWritesReport() throws Exception {
+		prepareTask("string/toUpperCase", (architectureCheck) -> {
+			assertThatExceptionOfType(GradleException.class).isThrownBy(architectureCheck::checkArchitecture);
+			assertThat(failureReport(architectureCheck)).isNotEmpty()
+				.content()
+				.contains("because String.toUpperCase(Locale.ROOT) should be used instead");
+		});
+	}
+
+	@Test
+	void whenClassCallsStringToLowerCaseWithoutLocaleFailsAndWritesReport() throws Exception {
+		prepareTask("string/toLowerCase", (architectureCheck) -> {
+			assertThatExceptionOfType(GradleException.class).isThrownBy(architectureCheck::checkArchitecture);
+			assertThat(failureReport(architectureCheck)).isNotEmpty()
+				.content()
+				.contains("because String.toLowerCase(Locale.ROOT) should be used instead");
+		});
+	}
+
+	@Test
+	void whenClassCallsStringToLowerCaseWithLocaleShouldNotFail() throws Exception {
+		prepareTask("string/toLowerCaseWithLocale", (architectureCheck) -> {
+			architectureCheck.checkArchitecture();
+			assertThat(failureReport(architectureCheck)).isEmpty();
+		});
+	}
+
+	@Test
+	void whenClassCallsStringToUpperCaseWithLocaleShouldNotFail() throws Exception {
+		prepareTask("string/toUpperCaseWithLocale", (architectureCheck) -> {
+			architectureCheck.checkArchitecture();
+			assertThat(failureReport(architectureCheck)).isEmpty();
+		});
+	}
+
 	private void prepareTask(String classes, Callback<ArchitectureCheck> callback) throws Exception {
 		File projectDir = new File(this.temp, "project");
 		projectDir.mkdirs();
diff --git a/buildSrc/src/test/java/org/springframework/boot/build/architecture/string/toLowerCase/ToLowerCase.java b/buildSrc/src/test/java/org/springframework/boot/build/architecture/string/toLowerCase/ToLowerCase.java
new file mode 100644
index 00000000000..bbdfd9abb3d
--- /dev/null
+++ b/buildSrc/src/test/java/org/springframework/boot/build/architecture/string/toLowerCase/ToLowerCase.java
@@ -0,0 +1,26 @@
+/*
+ * Copyright 2012-2024 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.build.architecture.string.toLowerCase;
+
+class ToLowerCase {
+
+	void exampleMethod() {
+		String test = "Object must not be null";
+		System.out.println(test.toLowerCase());
+	}
+
+}
diff --git a/buildSrc/src/test/java/org/springframework/boot/build/architecture/string/toLowerCaseWithLocale/ToLowerCaseWithLocale.java b/buildSrc/src/test/java/org/springframework/boot/build/architecture/string/toLowerCaseWithLocale/ToLowerCaseWithLocale.java
new file mode 100644
index 00000000000..1f3c3225cd0
--- /dev/null
+++ b/buildSrc/src/test/java/org/springframework/boot/build/architecture/string/toLowerCaseWithLocale/ToLowerCaseWithLocale.java
@@ -0,0 +1,28 @@
+/*
+ * Copyright 2012-2024 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.build.architecture.string.toLowerCaseWithLocale;
+
+import java.util.Locale;
+
+class ToLowerCaseWithLocale {
+
+	void exampleMethod() {
+		String test = "Object must not be null";
+		System.out.println(test.toLowerCase(Locale.ENGLISH));
+	}
+
+}
diff --git a/buildSrc/src/test/java/org/springframework/boot/build/architecture/string/toUpperCase/ToUpperCase.java b/buildSrc/src/test/java/org/springframework/boot/build/architecture/string/toUpperCase/ToUpperCase.java
new file mode 100644
index 00000000000..97d3ab61517
--- /dev/null
+++ b/buildSrc/src/test/java/org/springframework/boot/build/architecture/string/toUpperCase/ToUpperCase.java
@@ -0,0 +1,26 @@
+/*
+ * Copyright 2012-2024 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.build.architecture.string.toUpperCase;
+
+class ToUpperCase {
+
+	void exampleMethod() {
+		String test = "Object must not be null";
+		System.out.println(test.toUpperCase());
+	}
+
+}
diff --git a/buildSrc/src/test/java/org/springframework/boot/build/architecture/string/toUpperCaseWithLocale/ToUpperCaseWithLocale.java b/buildSrc/src/test/java/org/springframework/boot/build/architecture/string/toUpperCaseWithLocale/ToUpperCaseWithLocale.java
new file mode 100644
index 00000000000..0ac9d136051
--- /dev/null
+++ b/buildSrc/src/test/java/org/springframework/boot/build/architecture/string/toUpperCaseWithLocale/ToUpperCaseWithLocale.java
@@ -0,0 +1,28 @@
+/*
+ * Copyright 2012-2024 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.build.architecture.string.toUpperCaseWithLocale;
+
+import java.util.Locale;
+
+class ToUpperCaseWithLocale {
+
+	void exampleMethod() {
+		String test = "Object must not be null";
+		System.out.println(test.toUpperCase(Locale.ROOT));
+	}
+
+}