American Airlines' Transport Workers Union must vote whether to accept the airline's final contract offer.
Union workers began voting at 12:01 a.m., according the the union's website.
Under the latest contact offer to the union, if workers accept, it would save about 3,000 jobs that would otherwise be lost if the current bankruptcy plan moves forward The Tulsa World reports.
American Airlines filed for Chapter 11 bankruptcy in November 2011. The company wants to throw out union contracts and cut about 13,000 jobs. If the union doesn't accept the offer, a bankruptcy judge will determine the outcome. No matter how the union workers vote, jobs will still be lost.
The binding contract would last six years.
Union polls stay open through May 14.
NBC 5's Amanda Guerra contributed to this report.