THE AM for Blaenau Gwent Alun Davies yesterday denied allegations that he breached the ministerial code over the Circuit of Wales.
Tory AM Antoinette Sandbach has called for a formal investigation after reports said Mr Davies, who is natural resources minister, had contacted environmental body Natural Resources Wales in favour of the project.
NRW had been objecting to the scheme but later dropped its landscape and ecological objections.
Mr Davies is responsible for the body.
In a letter to Carwyn Jones, Ms Sandbach said she believed his actions to be a breach of the ministerial code, but Mr Davies yesterday denied the allegations that he had breached the code.
Mr Davies, who said he was aware of the letter from the media, said: "I haven't taken any decisions on this as a minister."
Reports emerged over the weekend that Alun Davies had told Natural Resources Wales in June last year by email that he was "very disappointed" with the approach the body had taken over Circuit of Wales.
In the two months following Mr Davies' email NRW told Welsh Government ministers that they didn't need to call-in the planning application.
Ms Sandbach's letter to Carwyn Jones says there appears to be a clear conflict of interest between Mr Davies' role as an AM and his role as a minister.
"There are grave concerns expressed clearly in the public domain that the conflict of interest in this case was overwhelming and that the minister in charge of the sustainable management of natural resources has placed consistency interests above the interests of sustainable management of the environment," she said.
She asked for full disclosure of any request made by the minister for Mr Jones' advice.
The Welsh Government confirmed it received Ms Sandbach's letter yesterday.