Bob Crow has described criticism of the holiday he took to Brazil last week as "a load of old cobblers", adding:
"I said I would be back if needed, but I have not been involved in the talks. It has made no difference whatsoever."
The RMT boss revealed his cruise holiday was advertised in the Daily Mail, the same paper which took a photo of him in his Bermuda shorts.
The confrontation came during the Mayor's monthly phone-in show on LBC 97.3 - thought to be only the second time the two men have spoken.
The dispute over ticket office closures was deadlocked tonight with millions of commuters almost certain to be caught in the crossfire.
London Underground says services will be affected from around 9:30pm on Tuesday 4 February.