Board members will meet in India on 29 March to discuss a move that would see 1,000 jobs axed across the UK, including 750 at Port Talbot.
But Community union members met Tata's European chief executive on Monday amid concerns the plant could be mothballed.
In January, Tata said "tough actions" were critical because of "extremely difficult market conditions".
Community's general secretary Roy Rickhuss said the likelihood of job losses had been "tough to accept" but workers were determined to make the proposal work.
He added: "Reports that suggest the Tata board in India will reject this turnaround plan are deeply concerning and Community will be doing all we can to ensure the company do not go down this route.
"The workers at Port Talbot have achieved everything asked of them and deserve the continued support of Tata."
Tata Steel could "pull the plug" on a plan to save Port Talbot steelworks, a union has warned.