Councils could be financially ruined if the hundreds of equal pay cases against north-east authorities inspire similar actions elsewhere, Unison has warned.
Solicitor Stefan Cross, a former Labour councillor at Newcastle City Council, said he had 450 cases pending at employment tribunals against Middlesbrough Council, and smaller numbers against others in the region.
He has sought back pay to 1997, when the national single status deal was struck.
Mr Cross has won cases on behalf of 140 Redcar & Cleveland BC staff, though the council disputes the impact of the ruling (LGC, 13 February).
He has argued that some single status agreements failed to address unequal pay, and is taking legal action against two Unison branch secretaries who signed agreements - Kenny Bell, of Newcastle, and John McCormack of Redcar & Cleveland.
Action is also pending against the Advisory Conciliation & Arbitration Service, which advised on the deals.
Unison local government head Heather Wakefield said the union would support its two officials, and did not want to pursue equal pay arrears to the point where other members' jobs would be jeopardised.
She said: 'The ideal would be to get six years' back pay, but if we did that everywhere local government would collapse. The cost would run into billions of pounds.
'Mr Cross does not care about the long term viability of council services.'
But Mr Cross said: 'That is a shocking position for Unison to take. Unison is running a campaign for equal pay but is afraid to take action.'