U.S. airlines sued federal regulators on Monday to stop enforcement of a landmark change in labor law that could make it easier for unions to organize at rail and air carriers.

The lawsuit, filed in federal court in Washington, D.C., by the Air Transport Association of America trade group against the National Mediation Board, said the rule change, under which union-organizing elections would be decided on the number of votes cast, was unjustified and violated the law.

The previous rule, which dated back 75 years, required a majority of an entire work group to approve unionization, effectively counting those who don’t vote as ‘no’ votes.

The National Mediation Board, which coordinates labor relations with airlines and rail companies under the Railway Labor Act, last week announced the new rule, which will take effect June 10.

The rule change was widely expected after the Obama administration gave the three-member board a Democratic majority last year.

The Air Transport Association said it would seek a hearing on a preliminary injunction prior to the effective date of the rule change. It also said it hopes to conclude the litigation over the next two months.

Member companies that joined the ATA lawsuit include Delta Air Lines Inc , package delivery giant FedEx Corp , AirTran Airways , JetBlue Airways and Alaska Airlines, a unit of Alaska Air Group.

The National Mediation Board “has offered no adequate or neutral justification for this sweeping rule change,” the Air Transport Association complaint stated.

It added the U.S. board did not follow proper procedures in changing the rule, and said the NMB also discriminated against workers’ rights to reject unions by failing to include a decertification process in the new rule.

The rule change was requested in September by the Transportation Trades Department of the AFL-CIO, which said union elections should be decided by those who vote.

“The few airline CEOs challenging the new rule are eager to retain the old system that was rigged against workers,” Edward Wytkind, president of the AFL-CIO unit, said in a statement on Monday. He called the lawsuit “baseless.”

The rule change could have near-term implications for Atlanta-based Delta, where union representation must be resolved for tens of thousands of workers after the 2008 purchase of Northwest Airlines. Delta was largely nonunion before it acquired Northwest.

“We believe that Delta and Delta people have been singled out for this rule change,” Mike Campbell, Delta executive vice president of human resources and labor relations, said in memo informing staff about the lawsuit on Monday.

Campbell added that the Association of Flight Attendants-CWA and International Association of Machinists and Aerospace Workers unions filed for representation elections at Delta last summer but withdrew those requests shortly after learning of the proposed change to the U.S. union-organizing rule in the fall.

“We believe this calls for court review,” Campbell said in the memo. (Reuters)