The Allied Pilots Association filed a lawsuit against American Airlines parent company AMR Corp. in bankruptcy court in New York on Tuesday.
The APA argues the airlines cannot throw out its contract through bankruptcy because its contract already expired in 2008.
Instead, the union said it wants to continue negotiating with American Airlines under current rules, which they say give them more options to reach a favorable deal.
American plans to layoff 400 pilots as part of its restructuring plan.
"We have just received the APA's filing, and we are confident in our legal position. We will need to review the filing in more detail before commenting further. We think it is unfortunate that APA has resorted so quickly to litigation rather than focusing on the bargaining table where there are pressing economic issues to be resolved," American Airlines spokesman Bruce Hicks said in a written statement.
NBC 5 is sorting through dozens of bankruptcy documents American Airlines filed in the last 24 hours.
Normally, the financial documents would have been submitted within 14 days of filing for Chapter 11 protection, but American got an extension.
The documents show American paid more than $12 million to advisers and firms for bankruptcy services in the last year.
American also listed losses that might be covered by insurance, including $7 million in hail damage to aircraft at Dallas/Fort Worth International Airport.
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