London Underground (LU) has denied union claims that Monday morning rush-hour "chaos" on the network was caused by an overtime ban.
There was major disruption on the Central and Metropolitan lines and minor delays on the District, Northern and Piccadilly lines.
The Rail Maritime and Transport union said these were due to the industrial action in a row over job cuts.
LU said the only line affected by the action was the Metropolitan.
It blamed the other delays on signal failures and over-running engineering work.
Members of the Rail Maritime and Transport (RMT) union and the Transport Salaried Staffs Association (TSSA) have already held two strikes and are threatening fresh walkouts next month, claiming Transport for London is now planning to cut almost 2,000 jobs.
RMT general secretary Bob Crow said: "This morning's chaos on a number of key Tube lines is mainly down to the combined impact of the ongoing RMT and TSSA overtime ban and has exposed just how reliant LU are on the goodwill of their staff to deliver a decent service.
"That goodwill has been destroyed by the attack on 2,000 Tube jobs and it is now down to the mayor and his officials to get their heads out of the sand and meet with us directly to resolve the growing transport crisis in London."
The unions claimed that Tube services were running slower and less frequently across the system as a result of the overtime ban.
An LU spokesman apologised to commuters, adding: "The RMT leadership's overtime ban was only a factor in delays on the Metropolitan Line, where the RMT leadership is trying to hamper routine maintenance.
"Despite their claims, staff on the Piccadilly and Northern lines are not involved in their pointless industrial action.
"We have given cast-iron assurances that our staffing changes are being delivered with no compulsory redundancies and no pay reductions, that every station with a ticket office will retain one and that all stations will remain staffed."