London mayor Mr Ken Livingstone has made an 11th-hour plea to union leaders not to go ahead with industrial action on the Underground.
The Rail, Maritime and Transport Union (RMT) was set to announce a series of go-slows, with trains travelling at speeds of just 10 mph on lines where staff have safety concerns.
The action, the first of its kind in an industrial dispute on the Underground, was expected to be announced this morning.
But a few minutes before the union's expected announcement, Mr Livingstone arrived at the RMT's London head office to meet officials including general secretary Mr Bob Crow.
It is believed the mayor pleaded with the union to pull back from announcing industrial action until the results of a safety review by London Undergrond were announced in a few days.
The mayor refused to tell waiting journalists why he had turned up at the last minute and would only say: "I am not here. This is not happening. It is just a figment of your imagination."