Rep. Jim Moran (D-Va.) has been a regular critic of the new building's location just off Interstate 395 and its potential impact on the travel times of hundreds of thousands of commuters.
He says today's vote could pave the way for a year-long delay in the building's opening.
"I would hope that we would be able to extend it by still a further year, but of course these authorizations are for one year so we have to take it one step at a time," he says.
The vote is on the National Defense Authorization bill, which includes a provision allowing the Secretary of Defense to delay seven Base Realignment and Closure [BRAC] projects -- of which the Mark Center is one.
The bill also includes an amendment from Moran that caps the number of parking spaces employees could use at the new building.
"If we don't have that parking cap included in the legislative language, then we're going to create a traffic nightmare," he says.
If the bill passes today, the Senate will still have to vote on it. Right now, workers are scheduled to arrive at the building on September 15.
Even if the Defense Authorization bill passes with the BRAC provision, there will still be a next step for assuring a delay for the Mark Center plan. The bill language would allow Defense Secretary Robert Gates to delay seven BRAC moves of his choice -- so the onus would still be on Northern Virginia to lobby for Alexandria's inclusion in that list.