Charlton have asked the Premier League to intervene in their dispute with Chelsea over the loan of Carlton Cole.
The Addicks expected the striker to return for a second season under the terms agreed for Scott Parker's transfer to Chelsea back in January.
But Aston Villa announced on Monday they had secured Cole on loan.
Charlton chief executive Peter Varney said: "This should be resolved between the clubs. It is regrettable we are now forced to involve the Premier League."
Charlton have also sought legal advice to confirm the conditions of the contract they signed with Chelsea.
"We were given a categorical assurance on 6 July by Peter Kenyon that Carlton Cole would not be loaned to another Premiership club following his decision not to return to Charlton," Varney added.
"We were therefore very disappointed and angry to learn from the media and the Aston Villa and Chelsea websites that he had joined Villa on loan.
"We have a very clear and specific contract with Chelsea in relation to the transfer of Scott Parker and associated loan arrangements."
Cole's agent Jonathan Barnett has claimed that Charlton only had first option on the player if Cole wanted to return to The Valley.
Chelsea chief executive Peter Kenyon defended his club's role.
He said: "We are disappointed with the comments from Charlton about this matter.
"We are confident that Chelsea has conducted itself properly in all aspects of the transaction.
"The matter will be resolved between the two clubs and the Premier League."