From DOT:

The New York City Department of Transportation is conducting major long-term maintenance and repair work on the Williamsburg Bridge. The following is a travel advisory detailing lane closures relating to upcoming construction activity…

In order to stage equipment and deliver material for the intermediate tower bearing replacement, temporary lane closures are required on:

Saturday May 30, 2009 from 4:00 a.m. to 11:59 p.m.
Saturday June 6, 2009 from 4:00 a.m. to 11:59 p.m.

Three lanes will be closed to facilitate the construction activity. Two Manhattan-bound lanes and two Brooklyn-bound lanes will be maintained at all times by reversing the north inner roadway.

(When has the Williamsburg Bridge not been undergoing major rehabilitation?)