WordPress at a glance
action is not described

pre_user_query action-hook . WP 3.1.0

Fires after the WP_User_Query has been parsed, and before the query is executed.

The passed WP_User_Query object contains SQL parts formed from parsing the given query.

Usage

add_action( 'pre_user_query', 'action_function_name_3235' );
function action_function_name_3235( $this ){
	// action...
}
$this(WP_User_Query)
The current WP_User_Query instance, passed by reference.

Where the hook is called

WP_User_Query::prepare_query()
wp-includes/class-wp-user-query.php 576
do_action_ref_array( 'pre_user_query', array( &$this ) );

Where the hook is used (in WP core)

Does not used.