Workers at the vast Port Talbot steelworks in south Wales will be made redundant within months as part of a plan to secure its future while cutting thousands of jobs, unions have warned.

At a meeting between bosses at Indian conglomerate Tata, which owns Britain’s biggest steelworks, and union representatives in London, plans to make large-scale redundancies in “months rather than years” were discussed, sources said.

Last week, the UK government agreed to a £500m support package for Tata Steel, with the company also expected to inject about £725m to help the transition to greener production methods.

About 3,000 jobs are expected to be lost across Tata’s 8,000-strong UK workforce as a result of the deal, which involves shifting from coal-powered blastfurnaces to less labour-intensive electric arc furnaces. Unions are attempting to avoid compulsory redundancies.

On Wednesday, a trio of Tata executives –Koushik Chatterjee, the chief financial officer; Rajesh Nair, the chief executive of UK operations, and Raghav Sud, the chief of financial strategy and governance – met representatives from the Unite, GMB and Community unions at the five-star St James’s Court hotel, which is owned by the conglomerate.

Sources said Tata had agreed to allow the unions to analyse its plans for the steelworks, and that the coke ovens at Port Talbot could close as soon as January.

Charlotte Brumpton-Childs, a GMB national officer, said: “Today’s meeting with Tata bosses was the first step in the long process of consulting meaningfully with our members over steel job losses.

“Tata must be completely open throughout this process and not shut themselves off from solutions which decarbonise steel without redundancies. This deal is not and must not be a fait accompli – workers had a voice.”

A spokesperson for the Community union said: “Last week’s announcement was a bad deal for our steel industry. We want to work with Tata and the government to deliver a decarbonisation strategy that respects our red lines and crucially protects our members’ jobs through ensuring a just green transition.

“There will be a series of consultation meetings, and we will be clear to Tata that we will do whatever it takes to protect our members’ interests.”

On Tuesday, the business secretary, Kemi Badenoch, told MPs on the business and trade committee that Tata was losing £1m a day on the steelworks.

She said: “The problem we are trying to solve is how do we make sure we don’t create a catastrophe in Port Talbot where everybody loses their jobs? That includes not just the 8,000 people that work for Tata but the rest of the supply chain. How do we regenerate the area? How do we make sure that we’re hitting carbon emissions? And this deal was the one that ticked all those boxes.”

A Tata Steel spokesperson said: “We believe our £1.25bn proposal for green steelmaking in Port Talbot will secure jobs, bolster UK steel security and help develop a green ecosystem in the region.

“We are committed to meaningful consultation with our trade union partners about these proposals and will listen carefully to their concerns.”