diff --git a/services/s3/src/it/java/software/amazon/awssdk/services/s3/ServerSideEncryptionIntegrationTestBase.java b/services/s3/src/it/java/software/amazon/awssdk/services/s3/ServerSideEncryptionIntegrationTestBase.java
index 32d7ba225af4..bb41b56bc020 100644
--- a/services/s3/src/it/java/software/amazon/awssdk/services/s3/ServerSideEncryptionIntegrationTestBase.java
+++ b/services/s3/src/it/java/software/amazon/awssdk/services/s3/ServerSideEncryptionIntegrationTestBase.java
@@ -16,6 +16,7 @@
 
 import static org.assertj.core.api.Fail.fail;
 import static software.amazon.awssdk.services.s3.S3IntegrationTestBase.createBucket;
+import static software.amazon.awssdk.services.s3.model.ServerSideEncryption.AES256;
 import static software.amazon.awssdk.testutils.service.S3BucketUtils.temporaryBucketName;
 
 import java.io.File;
@@ -25,6 +26,7 @@
 import org.junit.AfterClass;
 import org.junit.BeforeClass;
 import software.amazon.awssdk.services.kms.KmsClient;
+import software.amazon.awssdk.services.s3.model.EncryptionType;
 import software.amazon.awssdk.services.s3.model.ServerSideEncryption;
 import software.amazon.awssdk.testutils.RandomTempFile;
 
@@ -48,6 +50,14 @@ public static void setupFixture() throws IOException {
         createBucket(BUCKET_WITH_SSE);
         keyId = KMS.createKey().keyMetadata().keyId();
 
+        // Since April 2026, new S3 buckets block SSE-C by default. Unblock it for SSE-C tests.
+        s3.putBucketEncryption(r -> r
+            .bucket(BUCKET)
+            .serverSideEncryptionConfiguration(ssec -> ssec
+                .rules(rule -> rule
+                    .applyServerSideEncryptionByDefault(d -> d.sseAlgorithm(AES256))
+                    .blockedEncryptionTypes(b -> b.encryptionType(EncryptionType.NONE)))));
+
         s3.putBucketEncryption(r -> r
             .bucket(BUCKET_WITH_SSE)
             .serverSideEncryptionConfiguration(ssec -> ssec
diff --git a/services/s3/src/it/java/software/amazon/awssdk/services/s3/multipart/S3ClientMultiPartCopyIntegrationTest.java b/services/s3/src/it/java/software/amazon/awssdk/services/s3/multipart/S3ClientMultiPartCopyIntegrationTest.java
index 4d942d942e7f..51e467979f3e 100644
--- a/services/s3/src/it/java/software/amazon/awssdk/services/s3/multipart/S3ClientMultiPartCopyIntegrationTest.java
+++ b/services/s3/src/it/java/software/amazon/awssdk/services/s3/multipart/S3ClientMultiPartCopyIntegrationTest.java
@@ -50,6 +50,7 @@
 import software.amazon.awssdk.services.s3.internal.multipart.MultipartS3AsyncClient;
 import software.amazon.awssdk.services.s3.model.ChecksumAlgorithm;
 import software.amazon.awssdk.services.s3.model.CopyObjectResponse;
+import software.amazon.awssdk.services.s3.model.EncryptionType;
 import software.amazon.awssdk.services.s3.model.GetObjectResponse;
 import software.amazon.awssdk.services.s3.model.MetadataDirective;
 import software.amazon.awssdk.utils.Md5Utils;
@@ -71,6 +72,14 @@ public class S3ClientMultiPartCopyIntegrationTest extends S3IntegrationTestBase
     public static void setUp() throws Exception {
         S3IntegrationTestBase.setUp();
         createBucket(BUCKET);
+
+        s3.putBucketEncryption(r -> r.bucket(BUCKET)
+                                     .serverSideEncryptionConfiguration(c -> c.rules(
+                                         rule -> rule.applyServerSideEncryptionByDefault(
+                                                         d -> d.sseAlgorithm(AES256))
+                                                     .blockedEncryptionTypes(
+                                                         b -> b.encryptionType(EncryptionType.NONE)))));
+
         s3CrtAsyncClient = S3CrtAsyncClient.builder()
                                            .credentialsProvider(CREDENTIALS_PROVIDER_CHAIN)
                                            .region(DEFAULT_REGION)
diff --git a/services/s3/src/it/java/software/amazon/awssdk/services/s3/multipart/S3MultipartClientPutObjectIntegrationTest.java b/services/s3/src/it/java/software/amazon/awssdk/services/s3/multipart/S3MultipartClientPutObjectIntegrationTest.java
index aed75193c0ea..8967cb540e2c 100644
--- a/services/s3/src/it/java/software/amazon/awssdk/services/s3/multipart/S3MultipartClientPutObjectIntegrationTest.java
+++ b/services/s3/src/it/java/software/amazon/awssdk/services/s3/multipart/S3MultipartClientPutObjectIntegrationTest.java
@@ -78,6 +78,7 @@
 import software.amazon.awssdk.services.s3.model.ChecksumMode;
 import software.amazon.awssdk.services.s3.model.CompleteMultipartUploadRequest;
 import software.amazon.awssdk.services.s3.model.CreateMultipartUploadRequest;
+import software.amazon.awssdk.services.s3.model.EncryptionType;
 import software.amazon.awssdk.services.s3.model.GetObjectRequest;
 import software.amazon.awssdk.services.s3.model.GetObjectResponse;
 import software.amazon.awssdk.services.s3.model.PutObjectRequest;
@@ -110,6 +111,13 @@ public static void setup() throws Exception {
         setUp();
         createBucket(TEST_BUCKET);
 
+        s3.putBucketEncryption(r -> r.bucket(TEST_BUCKET)
+                                     .serverSideEncryptionConfiguration(c -> c.rules(
+                                         rule -> rule.applyServerSideEncryptionByDefault(
+                                                         d -> d.sseAlgorithm(AES256))
+                                                     .blockedEncryptionTypes(
+                                                         b -> b.encryptionType(EncryptionType.NONE)))));
+
         testFile = new RandomTempFile(OBJ_SIZE);
         bytes = Files.readAllBytes(testFile.toPath());
         expectedChecksum = ChecksumUtils.computeCheckSum(Files.newInputStream(testFile.toPath()));