The prospect of a legal battle between clubs and the Premier League has escalated after Sheffield United announced they are to join Wigan in preparing a possible case.

The two clubs have hired lawyers to assess whether they can take action against the league for West Ham not being deducted points after pleading guilty to breaching transfer regulations over the signings of Carlos Tevez and Javier Mascherano.

The Premier League have also taken legal advice and have been told their position is unassailable.

Sheffield United and Wigan are both preparing for possible legal challenges should they be relegated instead of West Ham.

The Blades plc chairman Kevin McCabe said he set lawyers on the case within hours of the verdict being delivered by an independent commission last weekend.

McCabe said: ''We took this course of action independently of anyone else in an attempt to try to protect ourselves should we suffer as a consequence of this bizarre decision.

''We have some excellent and reputable lawyers who have already been looking at this matter for us for a week.

''Obviously we hope that we don't suffer as a result, but we felt this needed to be done.''

Manchester United manager Sir Alex Ferguson believes Wigan and Sheffield United are right to pursue their course of action.

Ferguson said: ''It is nothing really to do with us but I do understand it. They have every right to take advice on it because it was a strange decision.''

The Premier League's position is that it is entirely up to the independent commission to decide on the punishment, and that if they had any influence over the decision it would be a conflict of interest.

They would argue the commission had a full range of sanctions available to it and that Premier League rules do not state what the punishment should be for such rule breaches.

A league spokesman said: ''We await to see what legal advice is received by the clubs.''

West Ham are also unconcerned by the prospect of possible legal action.

Chairman Eggert Magnusson has a great deal of experience of cases regarding player eligibility from his time in UEFA and FIFA, and never viewed the club's breaches - which took place before he took over - as likely to result in a points deduction.

Wigan chairman Dave Whelan believes the independent commission should have hit West Ham with a ten-point penalty after they found the club guilty on two charges of transfer irregularities, rather than fining them £5.5m.

Should the clubs pursue legal action, they will claim points penalties have been issued before for offences they would argue were less serious.

Middlesbrough were deducted three points a decade ago for failing to fulfil a fixture, a judgement that condemned them to relegation from the Premiership.