Dundee are to appeal the SPL's decision to fine Livingston £15,000 for a breach of transfer regulations.
Hassan Kachloul (left) played eight games for Livingston
The SPL ruled that Livingston were wrong to register Hassan Kachloul as an amateur but decided the club gained no real advantage from the mistake.
Kachloul was entitled to sign on professional terms on his March arrival because he was unattached to a club.
Dundee are angry Livingston have not been docked points that may have saved them from relegation.
The Dens Park club, who finished two points behind Livi, have called the ruling as a "charter for cheats." and say they will appeal against the decision to the Scottish Football Association.
Dunfermline and Dundee raised concerns after Kachloul arrived on an amateur contract, in a move designed to circumvent the transfer window regulations.
However, since the Moroccan midfielder was not leaving a club to join Livingston, there was no need for such an arrangement.
Kachloul played eight games for Livingston, including a nail-biting final day encounter against Dundee that ended 1-1.
An SPL statement said: "Livingston have been found to have been in breach of both of SFA Articles and registration procedures and the SPL Rules by registering Hassan Kachloul as an amateur player.
"But the Board identified that Hassan Kachloul would have been eligible to be registered as a professional player by Livingston on March 31, 2005 and to have played in league matches during the remainder of season 2004-05.
"As a consequence, Livingston secured no competitive advantage by having registered the player as an amateur, rather than as a professional, since the club would have been entitled, had due enquiry been made regarding Hassan Kachloul's contractual history and his position under the rules of football, to have registered the player as a professional.
"For breach of the rules of the SPL, the board have severely censured Livingston FC, warned the club about their need to comply with those rules in the future, and fined the club £15,000." Dundee have already threatened to go to the courts over the matter.
And the relegated club would seek to have former Livingston boss Richard Gough and players who have since left the club called as witnesses in any civil action.