The agreement, which brought to a close one of the most disruptive labor disputes to hit a top-four U.S. airline in more than a decade, came a day after rival U.S. carrier American Airlines Group Inc said it was filing a labor-related lawsuit against its mechanics.
Analysts have highlighted labor issues as a main concern for airlines this year, in addition to rising fuel costs and the grounding of Boeing MAX jets after two fatal crashes.
Mechanics at both American and Southwest have complained that the airlines are moving to outsource maintenance work that has traditionally been done in-house.
In a statement on its website, the Aircraft Mechanics Fraternal Association, which represents around 2,500 Southwest mechanics, said about 95 percent of its members had voted to accept a labor agreement that includes significant pay increases and headcount protections.
Southwest, which had been forced to cancel hundreds of flights earlier this year stemming from the mechanics dispute, welcomed the agreement.
"Our mechanics will receive well-deserved pay increases, and the company will realize additional flexibilities necessary to compete in today's airline industry," Russell McCrady, vice president of labor relations, said in a statement.
AMERICAN AIRLINES MECHANICS RESPOND TO LAWSUIT
Separately on Tuesday, American Airlines' mechanics union, the TWU-IAM Association, said it was "ready and willing" to return to the bargaining table to negotiate a fair contract, as long as it had a willing partner.
The comment followed a federal lawsuit filed by American alleging an illegal slowdown by its mechanics aimed at disrupting operations to improve their position in labor talks, which began in 2015.
"We would much prefer to be at the negotiating table than in a legal battle brought on by American," the TWU-IAM Association said in a statement.
American said the slowdowns had escalated following the last joint bargaining session on April 25, which was overseen by the National Mediation Board. The action has caused hundreds of flight cancellations and more than 1,000 maintenance delays, threatening further disruption during the busy U.S. summer, it said.
TWU-IAM, formed in 2015 after the merger of US Airways and American Airlines, said it wants to keep the company from outsourcing more maintenance and repair work to South America, China and Europe, and is "standing strong" against cuts to medical benefits and retirement security.
(Reporting by Tracy Rucinski; Editing by Susan Thomas and Bill Berkrot)
By Tracy Rucinski