Shadow Brexit Minister Keir Starmer is to demand answers in Parliament over what deal the Government offered Nissan to produce new models in Sunderland.
Workers, unions, politicians and business leaders were overjoyed last week when Nissan announced it would build the new Qashqai and X-Trail models at its Sunderland plant, allaying fears the plant would be hit by the impact of Brexit.
Nissan bosses had previously said they were holding off investment in the plant until the post-Brexit vision for Britain was clear.
The news, however, has raised questions among some over what, if any, deal the Government has made to keep Nissan sweet.
Now Shadow Brexit secretary Sir Keir Starmer has said will will seek to raise the issue in the House of Commons today, saying the Government still needed to disclose the full terms.
"There may be a financial element to it - I accept that. They say no money is changing hands. I don't know," he told ITV's Peston on Sunday programme.
"We need to know and I'm going to try and raise this in Parliament because something has been said.
"It's good Nissan are investing, of course it's good, but there are other businesses up and down the country of every size and every sort that need (reassurance)."
"They want to trade on the same terms and if there is a deal that's good enough for Nissan they are saying, and it's quite understandable, 'Well, we want broadly the same deal for us'."
His comments came after Business Secretary Greg Clark said it was assurances that the Government was committed to securing continued tariff-free access to EU markets which swayed Nissan.
However, he refused to be drawn on whether the Government was seeking to remain part of the EU customs union or on the implications for its commitment to end free movement of labour with the EU, saying it had yet to fully "crystallise" its negotiating position.
Appearing on BBC1's The Andrew Marr Show, he confirmed World Trade Organisation rules on state aid meant the Government could not offer to compensate Nissan if it was hit by new post-Brexit tariffs.
"It is simply not possible to compensate for any future risks so the intention of keeping the sector competitive was important," he said.
"What I said was that our objective would be to ensure that we would have continued access to the markets in Europe - and vice versa - without tariffs and without bureaucratic impediments and that is how we will approach those negotiations.
"For the continental European car manufacturers, they export a lot to us, we export a lot to them, components go backwards and forwards. If you conduct the negotiations in a serious, constructive and civilised way there is a lot in common that we can establish.
"I was able to reassure Nissan - and other manufacturers - that that is the way we are going to approach it."