Thousands of construction workers have backed industrial action up to strikes if employers refuse to give them a 2.7pc pay rise next month.
Members of Batu, Connect, Opatsi, Siptu and Unite voted in favour of action if the increase due under a sectoral employment order is withheld.
The vote comes after the High Court ruled that legally binding sectoral employment orders were unconstitutional.
A stay has been put on this judgment pending a Government appeal to the Supreme Court.
Connect and Unite revealed they have already served notice on more than 50 employers of plumbers, fitters and welders yesterday.
Unite regional officer Tom Fitzgerald said notice was served on the Mechanical Engineering and Building Services Contractors Association (Mebsca) division of the Construction Industry Federation.
He said this came after employers refused to commit to a 2.7pc pay rise that was due earlier this month for these workers.
"It is now up to the employers to resolve this dispute by paying their workers the agreed pay increases which fell due on September 1," he said. "Otherwise, they will face an autumn of determined industrial action."
Under a separate general construction sectoral employment order, a pay rise of 2.7pc is due on October 1.
Irish Congress of Trade Unions general secretary Patricia King said workers in the construction sector were determined that employers would not be allowed renege on their legal responsibilities.
A spokesperson for Mebsca said it asked unions to reconsider its proposal to defer the 2.7pc wage rise until March 2021, or a new sectoral employment order was in place.
"A new sectoral employment order would ensure that Mebsca members could compete on a level playing field by ensuring that the 2.7pc increase applies to all working in the sector," he said.
The spokesperson said Mebsca companies faced a very challenging environment in terms of Covid-19, economic contraction and a reducing work pipeline, and paying the increase would threaten their viability by placing them at a competitive disadvantage with companies not covered by the existing agreement.