Talks aimed at avoiding widescale redundancies at Aer Lingus are due to continue between Siptu and airline bosses today.
It follows the announcement of 500 planned redundancies at the flag carrier due to Covid-19.
Friday's announcement of up to 500 layoffs at the airline was described by SIPTU as"Pouring petrol on the fire of an already difficult industrial relations environment."
The airline has already announced it was to halve the pay and hours of most employees and laid off a number of staff, including those based at Shannon Airport.
Implementation of the measures had been due to begin yesterday.
The union's Aviation Sector organiser Neil McGowan said the company must allow time for proper negotiations and consultation on the planned layoffs.
Mr McGowan added talks could not take place in a productive way when 200 his union's members were already on temporary lay-off and over 1,000 have had their pay cut
Siptu's aim was, he said to ensure that "as many jobs as possible are kept... and that any losses at the company should be voluntary".