Salford City Reds have been charged by the Rugby Football League with fielding 14 players for a period during Saturday's win over Castleford.
If found guilty, the Reds face a fine and possibly even a points deduction.
A tribunal to determine if the club should receive any punishment will take place on Wednesday, 8 May.
Salford beat Castleford 34-30
in Brian Noble's first match as head coach to move above the Tigers and off the bottom of the Super League table.
In response to the charge, a Salford spokesman said: "We are communicating with our coaching staff, the players involved and the RFL to establish the sequence of events during last weekend's round.
"We will, of course, be assisting the RFL tribunal in any way possible, but at this point in time cannot comment further."