Justice secretary Jack Straw is under pressure over a £3,000 payment made by an energy company to an event in his honour.
The Sunday Times reports that Cantaxx Energy Ventures had paid the amount to fund a party celebrating Mr Straw's 25th anniversary as an MP.
The newspaper reports that the firm was hoping to build a £300 million underground gas storage facility close to the MP's constituency at the time which was turned down by the local council on environmental grounds.
A new application is being submitted now, according to the Times.
Conservative MP Ben Wallace has sent a complaint to the electoral commission and the standards watchdog over the donation.
He told the Times: "Jack Straw quite clearly benefited from this donation and it should have been properly registered."
A spokesman for the justice secretary said: "Mr Straw has never had any involvement with Canatxx's business whatsoever. Not before the event referred to, during it or after it."
In 2006, in response to a parliamentary question about whether Mr Straw had any links to Cantaxx, the MP disclosed that a dinner held in April 2004 had received funds from the company. The amount donated was not disclosed in the reply.
A spokesperson for Cantaxx told the Sunday Times it considered the donation to be "non political" and in honour of the Mr Straw's 25 years of service to Blackburn.