Taiwan is bracing for the possibility of another round of flight disruptions as union members from EVA Air and China Airlines (CAL) line up to vote on whether to pursue strike action.

The ballot comes after labor talks between the Taoyuan Flight Attendants Union (TFAU) and EVA’s management resulted in an impasse in April over a list of grievances varying from higher layover allowances for cabin crew and more rest time between flights to the inclusion of union representatives on the airline’s board and internal disciplinary committee.

Some 3,000 EVA Air employees have until May 26 to cast their ballots; CAL workers will vote between May 27 and June 6, while members from other carriers prepare to vote between June 3 and June 6. According to the TAFU, more than half of its 5,600 cabin crew members must vote in favor of industrial action for a walkout to go into effect. To address concerns about vote manipulation by non-EVA workers, the union has stipulated a clause that at least 2,621 EVA members must approve any vote to strike.

In a memo released last week, EVA announced it would suspend employee flight ticket discounts for strike participants as well as year-end bonuses and annual pay raises for all employees if the strike resulted in a financial loss for the carrier. In response, the TFAU has accused the airline of breaching labor union laws.

The Taiwan ballot marks the latest in a series of labor battles between union members and the country’s two largest carriers. In February, more than 600 CAL pilots, represented by the Taoyuan Union of Pilots, staged a walkout after a series of negotiations failed over longstanding disputes surrounding working hours and labor-law violations. The airline had to cancel more than 200 flights, resulting in more than $16 million in losses.

After seven days of strikes, pilots returned to work after the two sides reached a consensus on the majority of worker demands. Under the terms of the new deal, CAL agreed to increase the number of pilots from two to three on flights lasting more than eight hours; the company also agreed to increase the number of pilots on flights of over 12 hours from three to four. Meanwhile, CAL will impose a two-year ban on hiring foreign pilots except under extenuating circumstances and extend promotion priority to Taiwanese employees, although it would grant an exemption for foreign pilots currently living in Taiwan. In turn, the union agreed not to strike for the duration of the collective agreement, which remains in place until August 2022.

The Taiwan government now hopes to avert a second strike this year and has called for an ad hoc committee to meet with airline management and TFAU members. In the event of a strike, authorities have called on CAL to assist EVA Air passengers with transfers and extra flight operations to minimize schedule disruptions.