The RMT union has rejected an offer of additional payments for Tube staff working during the Olympics.
According to the union, London Underground offered a flat rate of £100 linked to “targets” and additional shift allowances for some staff.
The union says this was “divisive” and fell short of demands for a single rate payable to all staff throughout the Olympics and Paralympics period.
The RMT has also agreed Olympics payments of £500 for Network Rail staff and £600 for London Overground workers.
Negotiators are to hold further talks with LU.
General Secretary Bob Crow said he would “press our case for a flat rate, across the board payment which recognises the contribution of all staff throughout the high pressure Olympics period.”
Mr Crow added: “It is well documented that transport will be the biggest logistical challenge throughout the Olympics period with massive pressure on staff and services from moving millions of extra passenger journeys around Greater London and the South East.
“All we are calling for is a fair deal for all the staff involved in delivering the colossal transport challenge that we will be facing this summer.”