Barnet Council could be liable for tens of millions of pounds as it faces the first local authority equal pay claim ever launched in London.
GMB Union has begun proceedings on behalf of around 400 women working as school support staff at the council.
They say there are structural pay differences between members of staff working in roles staffed predominantly by women and those roles carried out mostly by men.
Barnet’s Refuse Staff, who are overwhelmingly men, currently receive a full day’s wages even if they complete their work early.
Some roles within the council’s Refuse Department have also been paid a retention bonus, which school support staff have not received.
GMB has attempted to settle the claim through negotiations.
Beverley Gunning, Barnet branch secretary at GMB, said: “It is shameful that we must take Barnet Council to court to make them do the right thing, but we will do whatever is necessary to fight for the money our members are owed after years of systemic gender pay discrimination.
“The work of school support staff is vital, and these members are already some of the council’s lowest paid staff.
“These loyal and committed workers deserve for Barnet to settle the full amount owed, set things right for the future, and issue an unreserved apology from the council.
“The longer it takes to settle this claim, the larger the settlement will grow.
“Barnet Council is running out of time.”
A spokesperson for Barnet Council said: “Barnet Council takes its equalities and equal pay responsibilities very seriously. We are always happy to meet with union colleagues.
“GMB is yet to set out which staff, at which grades, in which schools they believe have a claim.
“GMB has also overlooked that, while school staff in maintained schools are legally employed by the council, schools undertake their own recruitment, hold their own HR records, set their own recruitment and retention policies, and make local decisions about working practices.”