General Secretary Mick Cash said.
"This announcement has been dropped on London by the Mayor as a blatant pre election stunt without a shred of consultation with the union. That is a ridiculous way to conduct important negotiations and to unveil major service developments.
"RMT is not opposed to extended running but there are massive issues on staffing, safety and maintenance which have not been addressed and which would need to be signed off by our reps.
"This announcement has been made against the backdrop of a near doubling in assaults on staff, cuts to over a thousand jobs and the axing of guards on London Overground. Night running would mean increased drunkenness and risks to both passengers and staff alike and could only work with substantial increases in staffing right across the board and that means an immediate reversal of the current cuts programme . "