Derby County manager Nigel Clough has been charged with improper conduct relating to Saturday's 3-2 defeat by Peterborough United.
A Football Association spokesman said an incident during the game led to the charge - not Clough's post-match comments about referee Iain Williamson.
But the FA has refused to be more specific and Clough has until 1600 GMT on Friday, 11 November to reply.
The Rams boss was also highly critical of Williamson after Posh's late winner.
The 45-year-old told BBC Radio Derby: "We mark them [referees] out of 100 during the week. Based on his performance, he will get an extremely low mark."