Boeing has been under intense scrutiny following a dangerous incident on an Alaska Airlines flight last month, capping off a challenging five years for the aircraft manufacturer in the aftermath of two major crashes. But Boeing could be faced with yet another headwind as its largest union, the International Association of Machinists and Aerospace Workers, prepares for contract negotiations.

When negotiations begin in March, union leaders are planning to demand a 40% raise and are ready to go on strike if necessary, according to a Bloomberg report. (Negotiations were slated to begin this month but were postponed at the request of Boeing management, in light of its current business challenges.) They also intend to push for better health insurance coverage and pension benefits, as well as “more flexibility around overtime,” Bloomberg reports.

Previously, Boeing threatened to relocate manufacturing jobs during negotiations with its union.

This stance is partly driven by the deal union leaders were forced to ink back in 2014, which froze pensions and limited total pay raises to just 4% over a decade. At the time, Boeing used its 777X jet program to force the union to accept those conditions, in part by threatening to relocate manufacturing jobs.

But union leaders say they are emboldened by the significant uptick in strikes last year and the gains they saw workers make across sectors, from Hollywood to the auto industry. The negotiations also come at an especially fraught moment for Boeing, giving workers more leverage. Boeing is already reeling from manufacturing delays and expenses associated with the recent incident—which could total $1 billion, analysts told the New York Times—not to mention increased oversight from regulators and lawmakers.

To read more about Boeing’s showdown with union workers, click here.

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