There are concerns that thousands of job losses are set to be announced at Britain's biggest steelworks under plans to produce "greener" steel.
Tata has been in talks with the government for months over state aid worth hundreds of millions of pounds to help switch to electric arc furnaces that can run on zero-carbon electricity.
But unions fear the move could lead to around 3,000 job losses, mainly at Port Talbot.
In an announcement on Friday, ministers are expected to say the deal is intended to secure the survival of the plant which employs half of Tata Steel's 8,000-strong workforce.
Tata warned last year that its UK operations were under threat unless it secured government funding to help it move to less carbon-intensive electric arc furnaces.
Stephen Kinnock spoke to ITV Cymru Wales outside Tata Steel in Port Talbot
It is understood the UK Government is poised to announce a £500m subsidy alongside a £700m investment from the Indian company into the operations to help it move to greener forms of steel-making.
Unions representing workers at the plant have complained they had been shut out of negotiations over the deal.
Charlotte Brumpton-Childs, GMB national officer, said: "Government intervention in the steel industry is long overdue, but imposing a programme without proper worker consultation is unacceptable.
"GMB has urged ministers and Tata Steel to have a longer-term view on the decarbonisation of steel.
"It is not a just transition if thousands of jobs are sacrificed in the name of short-term environmental gains.
"We wholeheartedly support the move to modernise and decarbonise the industry, in fact we have sought this type of investment for years.
"But ignoring technologies outside of electric arc furnaces will mean tens of thousands of people will lose their livelihoods."
Alun Davies, national officer for the Community union, said: "There must be a full and meaningful consultation on all the options to decarbonise steelmaking and secure the future of every UK plant.
"Community will do everything within its powers to support our members and protect their jobs."
Gary Smith, general secretary of the GMB union told the PA news agency: "This deal will have devastating consequences for jobs and workers. It will rip the heart out of the Port Talbot community.
"For years, GMB has called for investment in this critically important industry. Instead of listening the Government dithered and delayed until it is too late, and thousands of workers, their families and communities will pay the price.
"Our country cannot be secure without a functioning domestic steel industry and workers must be at the heart of plans to modernise it.
"Once again, we see how so-called transitions are anything but fair or just for working people."
ITV Wales has contacted the UK Government for a response.
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