The deal brokered by the UK government for Nissan to stay in Sunderland post-Brexit is under scrutiny from the European Commission.
Officials in Brussels have confirmed they have been in touch with Whitehall to ask what promises the Japanese car-maker was made to persuade it to keep its business on Wearside.
Nissan's future on Wearside had been in doubt following the 'Leave' vote in the EU referendum, with Sunderland seen as one of the flagbearers of Brexit.
Business Secretary Greg Clark has said Nissan was told the government would seek tariff-free access to EU markets for the car industry, but insisted there was "no cheque book" involved in the assurances given to the company.
The announcement that Nissan is to build two key models - the Qashqai and X-Trail - in the UK has raised fears that the agreement might have breached EU rules preventing unfair state aid to companies.
The UK is not allowed to offer state aid, such as financial assistance, under EU rules that prevent countries from propping up companies to the disadvantage of competitors from fellow member states.
The commission can fine member states and force the company that has benefited to return any money.
A European Commission spokesman said: “We have seen press reports regarding this issue. As a result, the commission at services level is in contact with the UK authorities. Such exchanges of information are common.
“In this specific case, the UK authorities have not notified any support to Nissan for assessment under EU state aid rules. We have not taken any formal views on the matter.”
A spokesman for Nissan said it was a matter between the government and the European Commission.