XM Satellite Radio Holdings Inc. and Sirius Satellite Radio Inc. said Wednesday they have agreed to extend their merger agreement.

Washington, D.C.-based XM and New York-based Sirius have agreed not to exercise their rights to terminate the merger agreement by May 15. The companies have agreed to extend the merger agreement by two week periods unless either side notifies the other of its intention not to extend.

The closing of the transaction remains subject to the approval from the Federal Communications Commission and the satisfaction of all other applicable conditions.

The Justice Department has already approved the all stock, $4 billion merger, along with the shareholders of both companies.

The satellite radio companies announced plans to merge over 14 months ago.

Shares of Sirius, fell1 3 cents, or 4.8 percent, to $2.57 and XM Satellite shares slipped 51 cents to $11.15