Could a strike be looming at American Airlines?

Unionized mechanics at American Airlines, the second-largest U.S. carrier, have voted against ratifying a pay deal that was offered on May 5, possibly setting up a labor dispute.

The Transport Workers Union said on its website that 6,074 mechanics and related members of the union rejected the tentative agreement, with 3,371 members voting in favor. Members of Stores union also rejected the dea.

However, Maintenance Control Technicians ratified the contract, put forth by American Airlines and the Transport Workers Union, with 60 members voting in favor and 18 against.

Airline strikes are rare but are allowed under U.S. law if mediated negotiations are at a standstill. President Barak Obama has the authority to intervene and temporarily halt a strike once it has started.