The Football League were expected to receive the writ on Wednesday morning and the papers are believed to be in the hands of their lawyers.
Officials at the Football League were unavailable for comment. Ken Bates has taken his claim against the 15-point deduction to the High Court after claiming the League's decision to hand down the punishment was 'wrongful'.
An appeal by United directly to the Football League has already been rejected, while two requests for the Football Association to intervene were also unsuccessful.
Leeds had then intended to seek independent arbitration under FA rules, but the club abandoned that plan after Bates accused the governing body of 'evasive behaviour and delaying tactics', an accusation which the FA denied.