London Underground (LU) workers from one Tube line are to be balloted on industrial action over the sacking of a union activist.
The Hammersmith & City line will be affected
The man was seen coming out of a squash club while he was on sick leave but the Rail Maritime and Transport union (RMT) said he has medical proof saying sporting activity was part of his recovery programme.
RMT members who work on the Hammersmith and City line, used by 55,000 people a day, will be involved in the ballot and are being urged to support strikes in protest at the dismissal of the train driver.
General secretary Bob Crow accused the company of "scraping the barrel" in finding an excuse to sack the activist.
"The company has wasted public money snooping to catch the driver coming out of his squash club while off sick with an ankle injury," he said.
"Yet the driver concerned has produced evidence that both his GP and sports injury therapist advised him that an increasing amount of exercise would speed his recovery and therefore his return to work."
An LU spokesman said the union has launched an appeal against the dismissal but said it was "disappointed that the RMT has called this ballot when the disciplinary process is not yet exhausted."
Last week the same union threatened strike action claiming that 6,000 of its members are being "short changed" by two private companies in charge of LU's tracks and signalling.
The RMT is calling for staff employed by Metronet and Tube Lines to have a pay increase of 0.75%, which was awarded earlier this year, back-dated 16 months to bring them in line with LU workers.