Theauthority in charge of the $6 billion Dulles Rail project is expected to decide Wednesday whether to drop a controversial preference for a union-friendly labor agreement that has Virginia officials threatening to cut off funding.

Virginia and Loudoun County threatened to drop support of the rail project if the Metropolitan Washington Airports Authority continues to insist on a labor agreement for the project's second phase that gives contractors using union labor an advantage.

Board members claim the labor agreement does not favor unions but makes construction safer and cheaper. But Virginia officials say the agreement favors unions and violates Virginia's right-to-work laws.

Gov. Bob McDonnell wrote Monday to U.S. Secretary of Transportation Ray LaHood to remind him that state law prohibits Virginia from giving its promised $150 million to the project unless the airports board drops the labor preference.