Airbus workers in Flintshire will find out later whether their working week could be reduced by 10%.
The proposal comes after the firm announced last year it was looking to shed 1,435 posts at its Broughton plant.
A ballot of up to 3,500 members of the Unite union closes within hours with the result expected later at the site, which employs 6,000.
Airbus said it would comment after the vote.
Reducing the working week could help to avoid compulsory redundancies.
It is understood many workers have opted for schemes including voluntary redundancies, but between 350 and 400 posts are still under threat.
Staff on furlough
Union sources have said that if workers at the site vote in favour of the arrangement, it would mean a reduction of 10% in their hours.
Airbus would make up a third of the shortfall in salaries, although workers would lose about 6.6% of their pay.
The 12-month arrangement would be implemented when the UK government furlough scheme comes to an end.
In April, 3,200 staff were placed on the furlough scheme.
