From Facebook Developer Wiki

Description

Returns a list of users who were banned by an application using admin.banUsers.

Parameters

Required	Name	Type	Description
required	api_key	string	The application key associated with the calling application. If you specify the API key in your client, you don't need to pass it with every call.
	sig	string	An MD5 hash of the current request and your secret key, as described in the How Facebook Authenticates Your Application. Facebook computes the signature for you automatically.
	v	string	This must be set to 1.0 to use this version of the API. If you specify the version in your client, you don't need to pass it with every call.
optional	format	string	The desired response format, which can be either XML or JSON. (Default value is XML.)
	callback	string	Name of a function to call. This is primarily to enable cross-domain JavaScript requests using the <script> tag, also known as JSONP, and works with both the XML and JSON formats. The function will be called with the response passed as the parameter.
	uids	string	A JSON-encoded array of user IDs used to filter the result. The only user IDs that are returned in uids are those of banned users.

Response

An array of user IDs from banned users.