Steelworkers’ unions will ballot members on strike action in response to job losses at Tata Steel.
Community reached a formal mandate to let members vote on strikes, while Unite will hold a ballot on 1 March.
Tata has announced plans to reduce emissions at its Port Talbot site, putting nearly 2,000 jobs at risk.
Community boss Roy Rickhuss said the union was “prepared to fight for our industry”.
“Industrial action is always a last resort but Tata’s actions mean we now have to prepare for that eventuality,” said Mr Rickhuss for Community, the union representing the most steelworkers.
He said recent statements from Tata indicates the company is “determined to impose its devastating proposals”, making a “complete mockery of the ongoing consultation process”.
“There is still time for Tata to change their position, but as things stand we are heading towards a major industrial dispute,” Mr Rickhuss added.
“We are preparing for that ballot to take place as soon as is practically possible.
Unite said its plans for a ballot were complete.
“Unite will fully support its members during any industrial dispute, with any resources needed, including its multimillion pound strike fund,” said Unite general secretary Sharon Graham.
Tata Steel Port Talbot job losses
Tata has said 2,423 jobs across the UK are at risk, with 1,929 of those in Port Talbot, which employs 3,859 people.
The firm plans to replace existing, and heavily polluting, blast furnaces at the site with greener electric arc furnaces.
There will be a phased closure of the site’s two blast furnaces, with the first furnace and coke ovens expected to cease operation by the middle of the year.
A winding down of its remaining heavy-end assets will follow in the latter half of 2024.
Alun Davies, Community’s national officer for steel, said: “No worker ever relishes the prospect of going on strike” but that workers are “being pushed ever-closer to that option”.
“Tata’s plan represented the cheapest option on the table and it is bad for jobs, bad for the economy, bad for the environment and bad for national security. We will not accept it,” he said.
“We will not stand back and allow our livelihoods, our communities and the UK’s steelmaking capacity to be thrown on the scrap heap.”
Analysis by Huw Thomas, Business Correspondent
Just two weeks into the formal consultation with Tata and the major union representing steelworkers is clearly exasperated.
Community’s move towards industrial action is swift but not surprising.
It regularly floated the possibility of future strike action during months of talks with Tata, and the lack of any early progress during the formal consultation period has given it the opportunity to ratchet up the intensity of its opposition.
The union primarily represent workers in the heavy end of steelmaking in Port Talbot, those whose jobs will disappear along with the blast furnace production that houses them.
Its announcement comes on the eve of mass rallies staged by multiple unions in Port Talbot and Newport, where the aim is to harness further public and political support for their campaign to save steelmaking.
Tata Steel’s objectives seem clear and immovable, and the company is unlikely to make concessions in response to the rallies or a looming industrial dispute.
A Tata Steel spokesperson said: “Much of our existing iron and steelmaking operation in Port Talbot is at the end of its life, is unreliable and inefficient, and contributing to losses of £1.7m a day in the last quarter alone.
“Our restructuring proposals would mean that we are able to sustain the business as we transition to new electric arc furnace technology.
“We believe we have a very exciting future ahead, providing the high quality, low-CO2 steels that our customers in the UK and overseas are so desperate for.”
The UK government said it would help staff at a “concerning time for Tata’s employees”, adding it had committed £80m in direct support for those affected.
The Welsh government has called for further talks on a longer transition at Port Talbot to protect jobs.