More than 93 percent of mechanics who voted decided against the company's offer, the International Brotherhood of Teamsters said in a news release. The union said it will petition the U.S. National Mediation Board for the go-ahead to strike.
It was not immediately clear if a strike was likely or how long it would take the union to request the action.
The vote marks a setback in United's years-long effort to reach a joint deal with the technicians. It has yet to conclude a contract covering maintenance workers from both United and Continental since the carriers merged in 2010.
"At a time when United Airlines is incredibly profitable, it is clear that mechanics deserve a better offer from the company," Jim Hoffa, Teamsters General President, said in the statement.
Chicago-based United more than doubled its adjusted fourth-quarter profit from a year ago to $934 million. Its contract offer provided for an immediate 25-percent raise and bonus checks averaging $9,000, though the Teamsters expressed concern regarding wages for incoming mechanics.
"Although we are disappointed by this outcome we are eager to get right back to the table," said Oscar Munoz, chief executive of parent United Continental Holdings Inc, in a post on a public company website that is focused on labor talks.
Munoz has made boosting workers' morale a priority since taking on the airline's top job in September.
United and the Teamsters paused talks in October after rival American Airlines Group Inc announced a wage hike, resetting what they considered was an acceptable offer.
(Sudarshan Varadhan in Bengaluru and Jeffrey Dastin - Business Insider)