Sheffield United have confirmed they plan to sue West Ham for the cost of relegation from the Premier League.
The Bramall Lane club say they plan to go to the High Court to seek 'substantial compensation' from West Ham for their handling of the Carlos Tevez affair.
The Blades claim West Ham's former owners misled the Premier League about the original Tevez deal.
United have put the cost of relegation at between £30million and £50million.
Toby Craig, a member of the club's legal team, told Sky Sports News: "After careful consideration and discussion with our legal advisors, Sheffield United are today initiating legal proceedings against West Ham United to seek substantial compensation for our relegation from the Premier League.
"West Ham have admitted to lying to the Premier League in order to secure the registration of Javier Mascherano and Carlos Tevez, which is also a breach of West Ham's contract with all members of the Premier League, including Sheffield United.
"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 help it restore integrity for the reputation of English football which has been tarnished by this affair."
The Blades recently failed in a High Court bid to force new Premier League disciplinary action against West Ham.
The move came after an arbitration panel rejected their claim against the Premier League for failing to dock West Ham points over the transfers of Tevez and Mascherano.