The RMT yesterday cited a fresh incident in which a Central line train was allowed to continue running despite smoke pouring from a seized axle.
Tube bosses are resisting a demand from the union to introduce daily maintenance checks on all tracks after last weekend's derailments. At present, engineers walk the lines every 48 or 72 hours.
Pat Sikorski, the RMT's assistant general secretary, said that on October 11 station staff had repeatedly warned of smoke coming from a Central line train. But the driver was not informed for seven stops, when he was told he "might" have a problem and took the train out of service at Bank station. It emerged that seized bearings on the wheel had generated extreme heat, posing a risk of derailment and fire.
Mr Sikorski said the tube's public-private partnership should be unpicked before more "potentially disastrous" incidents emerge: "How many more do we need before these crazy contracts are suspended?"
If RMT members vote for action, a series of 24-hour stoppages could disrupt services in the run-up to Christmas.
Tube Lines, which runs the track where Sunday's Camden Town derailment took place, said the RMT had refused to meet and discuss its demands.
London Underground's managing director, Tim O'Toole, criticised the RMT's demands this week by pointing out that tracks at the site of both of the weekend's derailments, at Hammersmith and Camden, had been inspected fewer than 24 hours previously. It was difficult to see how more visual checks could be a "useful solution" but he suggested that more ultrasonic inspections could be appropriate.
Appearing before an emergency session of the London assembly's transport committee, LU's safety director, Mike Strzelecki, said the number of derailments and broken rails had fallen since daily checks were abandoned in 1996.
But the drivers' union, Aslef, revealed it had advised members to refuse to drive, or cut their speeds, if they had any concerns.
