Charlton, Fulham, Sheffield United and Wigan have confirmed they are taking legal advice following the Premier League's decision not to deduct West Ham points over the transfers of Carlos Tevez and Javier Mascherano
West Ham escaped a points deduction despite breaking transfer regulations regarding the signings of Tevez and Mascherano.
The Upton Park outfit were fined £5.5m but not deducted points much to the anger of their relegation rivals.
Representatives of all four clubs are believed to have held a meeting in Harrods on Friday to discuss their plans to mount a legal battle.
Wigan chairman Dave Whelan revealed on Thursday that his club was considering taking legal action against the Premier League should West Ham avoid relegation.
Sheffield United chief Kevin McCabe also confirmed on Friday that he had a legal team working on the matter.
Now Fulham and Charlton have joined the legal battle to see if they have a case against the Premier League's ruling.
The four clubs claim the Premier League have set a precedent by not docking West Ham points for breaking transfer rules.
A statement released by the four clubs and sent to the Premier League's board of directors confirmed: "You should understand we are separately in the process of obtaining legal advice arising out of the terms of the decision.
"You can expect to hear from us in relation to this in the early part of next week.
"In the meantime, all our rights in that respect are reserved."
The statement from the clubs continued saying: "The board are given power under the rules to `inquire into any suspected or alleged breach of these rules...
"The FAPL have a duty to act in good faith and with reasonable diligence.
"That duty extends to investigating an alleged breach of the rules where there is some apparently credible evidence of a breach.
"Furthermore, given the potential significance to our clubs of any further serious breach of FAPL rules by West Ham at this point in time, not to investigate immediately would be a breach by the League of their obligation of utmost good faith to us under FAPL rule B13.
"In the light of the above it is incumbent upon the board forthwith to investigate this matter."
The Premier League, who have taken legal advice, have said they will study the letter from the four clubs before making a response.
A Premier League spokesman said: "We will study the contents of the letter and respond accordingly."
West Ham United si liaox..
As expected, it's only those clubs that are battling relegation who are suing. I understand their POV though.