BP is fighting against claims made by the US Federal Energy Regulatory Commission that its traders have been involved in manipulating natural gas prices.
The allegations come as another blow to the oil giant that is currently facing trial for the 2010 Deepwater Horizon disaster.
If the natural gas market manipulation claims are to be confirmed, BP would have to pay a $28.8m (£18.8m) fine.
FERC has now given the company 30 days to provide explanation.
BP said the allegations were "without merit" and that it stood by its previous statement "that BP natural gas traders did not engage in any market manipulation in late 2008".
However, compared with the $42.4bn (£27.7bn) bill BP is supposed to have to pay in compensations for the Deepwater Horizon disaster, the current fine is rather insignificant.
In a separate trial, BP is trying to achieve reduction of the amount it is supposed to pay in compensations, pointing to the lack of transparency in the case.
Yesterday, the company has said it acquired substantial evidence of fraud having been committed, as two lawyers reviewing appeals of disputed claims were partners at law firms representing claimants before the Court Supervised Settlement Program (CSSP), and thus had apparent conflicts of interest.
It also said it learned through its fraud hotline of allegations that a worker at a Mobile, Alabama spill claims centre helped people submit fraudulent claims in exchange for a share of the settlement amounts. BP said the CSSP suspended two employees in connection with this matter.
Last week, BP chief Bob Dudley said it would dig in for a long-haul legal battle over more than a billion dollars of claims being handled by an administrator it said were absurd as they were from businesses that did not suffer losses.
BP’s profits slumped in the second quarter by 28 per cent to $2.7bn (£1.8bm), according to results published last month. The company said the loss was due to lower oil prices and a higher tax bill.