TATA Steel workers have been urged by AM Adam Price to reject the current pension deal that will be voted on later this month.
The Plaid Cymru Shadow Cabinet Secretary for Business, the Economy and Finance, claimed the deal currently on the table was "unacceptable" and that workers should ask Tata to rethink its offer on the employment pact and investment.
He also accused Tata Steel of being opportunistic in its offer.
"In my view the terms of the proposals on the table are simply unacceptable," he said.
"They are weighted far too heavily towards the company with the £1 billion investment reportedly contingent upon Tata Steel UK making a profit of £200 million each year.
"On top of this, the language of the employment act is highly dubious - seeking to avoid redundancies is not a concrete guarantee - and the company is seeking to walk away from its responsibilities to the 130,000 members of the British Steel Pension Scheme.
"It seems as if the company is using the events of the last 12 months to pressure workers to accept what is in reality an unacceptable deal.
"In my view the workers would be wise to ask the company to think again, and to come back to the table with a firm guarantee in terms of the employment pact and the investment.
"If Tata is not prepared to do this, the company should be nationalised on a temporary basis and talks reopened with those firms that have been waiting in the wings to buy it."
But chairman of the Port Talbot multi-union committee, Alan Coombes, said Mr Price's comments were not helpful at this point.
"It's a difficult one. I understand where he is coming from but he has not been involved in the discussions," he said.
"I understand his comments but they are not helpful at this point. People need to understand what is happening with their pensions and I would urge them to go to the ongoing meetings about that."