Updated

The Obama administration is again facing criticism from Big Labor, one of the president's top political supporters, this time for trying to block the American Airlines-US Airways merger.

At least four labor unions have joined in opposition to the Justice Department's Aug. 13  anti-trust suit that essentially argues the proposed, $11 billion merger could reduce the number of flight choices for customers, allow the two airlines to control pricing, and increase fares and fees.

Unions representing American pilots and flight attendants from both airlines were, as expected, the first to criticize the administration and the suit.

But the AFL-CIO’s Transportation Trade Department recently joined the fight, putting some added muscle behind opposition to the administration's case.

“It’s going further than just a few unions that really don’t represent a lot of people,” Marc Scribner, a transportation policy expert with Washington-based Competitive Enterprise Institute, told FoxNews.com on Monday.

In just the past several months, unions have criticized the president’s signature health care law as a jobs killer, claiming the law's mandate on employers to provide insurance to full-time workers is forcing them to cut jobs or send people into part-time status. They've also ripped the administration for not approving the Keystone XL pipeline and for a proposal to allow small knives in plane cabins, which representatives for pilots and flight attendants helped defeat.

The Allied Pilots Association, which represents 10,000 American Airlines pilots, argues the merger would make the two airlines competitive with industry leaders Delta and United, help bankrupt American Airlines and “significantly expand the choices of travel destinations.”

Further, they question why the federal government is attempting to block this merger after approving similar ones.

"It makes no sense for the Justice Department to conclude now that the airline industry consolidation is somehow undesirable,” argues the pilot’s union, which has the backing from unions representing flight attendants from both airlines.

Assistant Attorney General Bill Baer said in filing the suit: "We determined that the merger -- which would create the world’s largest airline and leave just three legacy carriers remaining in the U.S. -- would substantially lessen competition for commercial air travel throughout the United States. Importantly, neither airline needs this merger to succeed. We simply cannot approve a merger that would result in U.S. consumers paying higher fares, higher fees and receiving less service."

The Association of Flight Attendants, which represents US Airway attendants, called the suit a “war on workers.”

Scribner thinks Obama’s course of action on the recent issues is “definitely a risk,” considering Big Labor has long supported Democratic candidates.

The AFL-CIO contributed more than $9 million in 2011-12, and transportation unions gave roughly $11 million, second only to public sector unions over the same period, according to the website OpenSecrets.gov.

“There have been a number of various issues about which unions rightly feel upset,” Scribner added. “The president is doing things that don’t cater to the interests of labor.”

However, Big Labor abandoning Democrats in large numbers is not expected any time soon.

An internal poll by the AFL-CIO on election night 2012 showed Obama got roughly 65 percent of the union vote, compared with 33 percent for Mitt Romney, with larger margins in battleground states.

The federal suit was joined by the District of Columbia and six attorneys general -- including Virginia's Ken Cuccinelli and Greg Abbott of Texas, both Republicans, who are both running for governor.

The airlines have filed a motion in court seeking a November trial date.