The leader of the union at the centre of an impending Tube strike has resigned from the Transport for London (TfL) board after a row with the mayor.
Mr Crow said he was "shocked" by Livingstone's comments
Rail, Maritime and Transport (RMT) general secretary Bob Crow was annoyed by Ken Livingstone's comments about next week's 24-hour strike.
He said, if he were an RMT member, he would cross picket lines on Tuesday.
Mr Crow said he could not, "in all conscience" remain on the board of the mayor's transport authority.
He said he had been "shocked, saddened and disappointed" by Mr Livingstone's comments.
"I was brought up according to Labour movement principles and to believe that the 11th commandment is `thou shalt not cross a picket line'," he said.
"The mayor should know that the way to settle disputes is not to attempt to break strikes but to negotiate, and that is what he should be getting his management to do."
The walk-out, which begins at 1830 BST on Tuesday, is expected to cause huge disruption for passengers on London Underground.
A simultaneous strike on the railways was called off on Thursday evening following a talks between Mr Crow and Network Rail's chief executive John Armitt.
Mr Crow said Mr Livingstone should follow Network Rail's example by getting executives involved to try to resolve the pay dispute.
But the mayor said the offer of a two-year pay deal worth 6.5% and a pledge of achieving a 35-hour week was "extremely generous" and should be accepted.
But union leaders said there were "major strings" attached and are pressing on with the strike.
Speaking at his mayoral question time on Thursday, Mr Livingstone said: "This position I find completely and utterly unacceptable.
"I have a long history of defending trade unionism... Londoners should not be put to this inconvenience and disruption."