Sheffield United are to sue West Ham for the cost of their relegation from the Premier League.
United were relegated after the Premier League opted not to dock West Ham points after they were found guilty of breaking League rules over the signing of Carlos Tevez.
Sheffield United have estimated the cost of their relegation at between £30m-£50m.
A Blades spokesman said: “After consideration and discussion with our legal advisers Sheffield United are today initiating legal proceedings against West Ham United.
“We are seeking substantial compensation for our relegation from the Premier League.
“This action is distinct from the arbitration proceedings between the club and the Premier League during the close season.
“We have always said that we will do everything in our power to secure justice for Sheffield United and restore the integrity of English football which has been tarnished by this affair.
“Once proceedings have been issued we will await a response from West Ham before making any further statements.”
The club recently failed in their High Court bid to force the Premier League to take disciplinary action against West Ham.
The legal moves came after an arbitration panel rejected the Blades’ claim that West Ham should have been docked points for breaking League rules when they signed Tevez and Javier Mascherano.
The panel fined West Ham £5.5m after the club had committed “an obvious and deliberate breach of the rules” and held them “responsible for dishonesty and deceit”.