The union for about 7,000 former Northwest Airlines flight attendants has sued Delta Air Lines, which bought Northwest in late 2008.
The Association of Flight Attendants alleges Delta is violating contractual rules about scheduling, workplace safety, hotel accommodations and other work matters.
The union is asking the U.S. District Court in Washington, D.C. to order a halt to the alleged violations and force Delta to follow the union contract. Atlanta-based Delta said the lawsuit has no merit and is meant to divide flight attendants.
The lawsuit comes as the union tries to ensure its own survival. While the former Northwest attendants are unionized, the Delta flight attendants aren't. Eventually, there will be an election to determine if all of the attendants will be unionized or not.