The BlockWorker operation allows you to prevent a Worker from working on your HITs. For example, you can block a Worker who is producing poor quality work. You may block up to 100,000 Workers.

You need the Worker ID to use this operation. You can get the Worker ID in the assignment data returned by a call to the GetAssignmentsForHIT operation. If the Worker ID is missing or invalid, this operation returns with the failure message "WorkerId is invalid." If the Worker is already blocked, this operation returns successfully.

A blocked Worker can view your HITs, but sees the following message under the Additional Information label:

The Requester (<Requester Name>) has chosen to prevent you from working on any of this Requester's HITs. 
There are a variety of reasons for Requesters to prevent particular Workers from completing their HITs.

If a Worker is working on a HIT when the block occurs, the Worker can submit the HIT but will not be able to work on any additional HITs.

To unblock a Worker use the UnblockWorker operation.

The following example of a call to the BlockWorker operation blocks a Worker from working on your HITs.
&AWSAccessKeyId=[the Requester's Access Key ID]
&Signature=[signature for this request]
&Timestamp=[your system's local time]

A request to the Mechanical Turk Service includes parameters that control its behavior and the data it returns. Required parameters must be included for the request to succeed.

BlockWorker accepts parameters common to all operations. Some common parameters are required. See Common Parameters for more information.

The following parameters are specific to the BlockWorker operation:

Operation The operation you want to call. To access the BlockWorker operation, set the Operation parameter to BlockWorker. Required BlockWorker
WorkerId The ID of the Worker to block. The Worker ID is included in the assignment data returned by a call to the GetAssignmentsForHIT operation. Required A valid Worker ID
Reason A message explaining the reason for blocking the Worker. This parameter allows you to keep track of your Workers. The Worker does not see this message. Required A string

A successful request for the BlockWorker operation will return with no errors. The response will include a BlockWorkerResult element, which contains the Request (if the Request response group is specified). The operation returns no other data.