FedEx Corp.’s unionized pilots will begin voting this week whether to authorize a strike, ratcheting up pressure in contract negotiations that have dragged on longer than expected.

The vote on strike authorization for the almost 6,000 pilots at FedEx’s Express unit will begin on April 18, according to a statement by the Air Line Pilots Association. The contract talks have been going on since May 2021.

“We do not make a decision like this lightly, but we intend to send a strong and unified message to management that our pilots are willing to go the distance to achieve the contract we have earned,” said Chris Norman, chair of the FedEx ALPA Master Executive Council, in the statement.

FedEx said in a statement that it’s “still in productive negotiations” with the pilots’ union and calling for a vote won’t impact any services.

Authorizing a strike is a common step in labor bargaining and can help increase the urgency of talks. FedEx pilots, though, fall under the Railway Labor Act, which doesn’t allow for the union to unilaterally declare a strike. The law requires the National Mediation Board to attempt to bring the two parties together and there is no set time for how long that takes.

FedEx and the union have been in mediated talks since October.

A pilots’ strike would be the first for FedEx and could threaten plans by new Chief Executive Officer Raj Subramaniam to cut $4 billion in costs by 2025. With the exception of drivers at one Freight-unit facility, pilots are the only group that has unionized at FedEx, according to the company’s annual report. The courier’s main rival, United Parcel Service Inc., has the largest private unionized workforce in the US.

“It’s time for FedEx management to get serious at the bargaining table and conclude negotiations with an agreement our pilots will support,” Norman said. 

If the National Mediation Board declares the negotiations are at an impasse, only then does the clock start ticking on cooling-off periods that could lead to a strike. The law allows President Joe Biden to intercede and set up a Presidential Emergency Board to make non-binding recommendations on how to resolve the impasse. If those recommendations are rejected, Congress then has the authority to step in and head off a strike.

Congress in December intervened in railroad union negotiations only days before more than 100,000 rail workers were set to strike.