London mayor Boris Johnson believes the battle to replace union boss Bob Crow may be driving tonight's Tube strike.
Mr Crow, the General Secretary of the RMT, died in March, just five weeks after the last strike over ticket office closures.
RMT members will beging a 48-hour strike at 9pm following the breakdown of last-ditch peace talks at the conciliation service ACAS.
Mr Johnson said an internal union struggle to succeed Mr Crow may explain the RMT's hard line.
"Some people might speculate the reason the RMT are not at the table in the way that they should be - I urge them to get to the table - is that they are engrossed in their own politicking because they have a leadership vacancy that they need to fill.
"It seems to me that may be the difficulty we are experiencing at the moment."
But RMT Acting General Secretary Mick Cash dismissed the mayor's comments.
"It's complete and utter nonsense and it's actually a distraction put about by London Underground and others to try and deflect from the real arguments which is about every booking office closing."
Boris Johnson described ticket offices as "heritage items" and said the Underground needed to move on.
"I would say to Londoners this is something that is going to save us huge sums of money that we'll be able to invest in a better service, help to keep fares down."