Workers are voting on temporary changes to terms and conditions as part of an impending sale of a giant steel plant.
Union members at Tata's Scunthorpe site are being balloted on a 3% cut in pay and a reduction in pensions, part of a "transformation plan" ahead of the expected sale to investment firm Greybull Capital.
Negotiations over the sale of the plant, which employs around 4,000 workers, have been taking place for several months, well before Tata announced last week that it was selling all its UK assets.
Steve McCool, national officer of the Community union, said terms and conditions at Scunthorpe would be restored after a year.
"We are hopeful that the deal between Tata Steel and Greybull can be completed soon. Our own independent experts, Syndex, have found the transformation plan to be robust with a high probability of success. Our experts have also advised us that Greybull has the necessary capabilities to deliver the plan and secure a sustainable future for the business.
"Having given all the proposals and the context full consideration, myself and the national officers from the other unions are recommending that our members vote for the temporary changes to terms and conditions on the basis that this will give the transformation plan with Greybull a greater chance of success," he said.
Members of Unite and the GMB are also being balloted, with the result due on April 19.
Community said negotiations with managers at Tata's Long Products division over the transformation plan had been difficult.
Meanwhile, the Business Secretary was in Mumbai to hold talks with Tata as part of efforts to save thousands of jobs.
Sajid Javid was meeting Cyrus Mistry, chairman of the Indian conglomerate, to discuss the planned sale.
The head of a group which could rescue steel plants and save thousands of jobs said he is aiming to avoid any redundancies if a deal is agreed.
Sanjeev Gupta, the head of the Liberty Group, held talks with the Government and has raised hopes that jobs could be saved, especially at the huge plant in Port Talbot, South Wales.
Mr Gupta said: "UK Government appears highly supportive and is proactively engaged in finding a long-term solution. We have also actively engaged with Welsh Government and again we are encouraged by their approach.
"The next step is for Tata to define the formal sales process and request indications of interest from potential buyers. We await further details on this and then will assess our own next step.
"Liberty has already proven its ability to build value from UK steel assets with our acquisition of our Newport Steel plant, Midlands engineering operations and most recently in Scotland where we acquired mills from Tata. Everyone is very motivated to find a solution."
Leaders of Community, Unite and the GMB spent an hour with Mr Javid before he left for Mumbai, stressing they wanted the Tata business sold together rather than firms "cherry-picking" different parts.
Unite leader Len McCluskey said it was a "good first step", adding that unions would work with the Government and any prospective buyers.
"At the moment we are on the same page. The Government needs to put a protective arm around the industry to show they are serious. Talk is cheap - we now need to see a practical application."
Community's general secretary, Roy Rickhuss, said unions wanted Mr Javid to stress the need for Tata to act responsibly as a search for a buyer continues.
Dave Hulse, national officer of the GMB, said: "Sajid Javid was asked to seek assurances from his meeting in India with Cyrus Mistry that Tata Steel was fully committed to being a responsible seller and that the time needed to find a buyer would be supported."