US firm Sidley Austin Brown & Wood’s age discrimination battle with 32 former equity partners is facing a key judgment that is likely to decide the outcome of the most high profile US partnership dispute in recent memory.

Three appeal judges are to decide whether Sidleys must hand over documents outlining its treatment of 32 partners who were demoted in October 1999 by the legacy Chicago firm Sidley & Austin as part of a bid to raise partner profits.