According to the Aircraft Mechanics Fraternal Association, 34 of the 37 eligible employees cast a ballot on the contract terms, with 19 voting against.
Negotiators for the two sides reached a tentative agreement on a new contract in October after more than three years of talks.
The Dallas-based carrier did not say when negotiations will resume.
“The company will take a step back to assess the results of the vote and determine how we might structure a contract that respects and serves the interests of both the company and our employees," said John Zuzu, Southwest’s senior director of corporate facilities.
(Conor Shine - The Dallas Morning News)