The UK will press for “job guarantees” in return for taxpayer-funded investment during talks with the Indian-owned Tata Steel about the future of its flagship Port Talbot site.

The new business secretary, Jonathan Reynolds, said he believed there was a “better deal available” for the south Wales site and the steel industry as a whole, as he confirmed on Sunday that negotiations with Tata were continuing.

His comments follow the steelworks’ future becoming a general election issue, after Labour and the Conservatives developed competing responses to Tata’s rejection of a trade union plan to keep Port Talbot’s blast furnaces running.

The company outlined in January that it could no longer afford to continue production at the loss-making Port Talbot plant – which it said was losing it £1m a day – while it completed a four-year transition plan towards greener production.

Tata and the former Conservative government agreed a deal last year where the company would receive £500m in state subsidies to help with the move to new “greener” furnaces, which could cut UK emissions by about 2% if renewable electricity was used.

However, the deal also involved closing the blast furnaces, putting 2,800 jobs at risk and potentially leaving the UK as the only big economy unable to make steel from scratch.

“There is a better deal available for Port Talbot and the steel industry as a whole,” Reynolds told BBC1’s Sunday With Laura Kuenssberg.

“There is more money available for the steel industry under our plans for government … But that’s about making sure we meet this transition with the private sector together … it is a good exemplar of how we have to make sure decarbonisation is not deindustrialisation, and we’ve got to do that together.”

The minister added: “I’m going to make sure that job guarantees are part of the negotiation that we’re having.”

Unite’s general secretary, Sharon Graham, told the same programme: “There’s no doubt that Labour coming in and the intent of what they want to do is a good thing.”

She added: “My main focus is jobs, pay and conditions for workers, so I’m going to either be seen as a critical friend or a pain in the proverbial … it’s my job to make sure feet to the fire on this.”

Labour has committed to provide £2.5bn to “rebuild our steel industry”, with Reynolds noting this was “on top of” the £500m committed by the previous government.

Tata has said it would make every effort to mitigate the impact of the transformation on affected employees and the local community, adding that it had put forward the most favourable financial package of support it had ever offered.

In a separate interview, Reynolds said the online fashion retailer Shein would be expected to meet “ethical and moral targets” on tax and all aspects of business if it listed on the London Stock Exchange.

He told Times Radio that he was “concerned” about a “loophole” that allowed firms to avoid import duties by shipping small packages directly to customers, and that he would want to discuss the issue with the company, which was founded in China.