Spectators heading to the London Olympic Games could have their travel plans disrupted by industrial action on the Tube.
London Underground employees are to stage a work-to-rule from Friday in an Olympics-related dispute.
The Rail, Maritime and Transport (RMT) union, which represents thousands of Tube staff, said it was in dispute over implementing an Olympics pay deal, as well as the use of casual workers.
The union also announced a strike by cleaners on the Tube and Docklands Light Railway (DLR) from Friday morning until Sunday, the first weekend of the Games.
LU said the action would have no impact on services.
The union said its members working as cleaners for contractors on the Tube and DLR will strike for 48 hours from Friday morning after voting for action over Olympics payments.
From Friday until further notice, all RMT members on the Tube are instructed not to work outside their job description.
RMT general secretary Bob Crow said: "While the ... the Government, are sitting in the well-padded VIP seats in the Olympics Stadium as a nice little bonus, our cleaners on the Tube and DLR, who work round the clock in appalling conditions, are being treated like dirt over recognition for the extra workload they will carry from the millions of extra passenger journeys associated with the Games.
"Even at this late hour there is time for the cleaning companies, and Mayor Boris Johnson, who hires them, to settle this dispute which is about ensuring an inclusive Olympics where everyone shares in the benefits.
"Meanwhile, our wider London Underground membership will be taking action short of a strike in defence of the existing casualisation dispute settlement and to protect their position in light of problems with the implementation of the Olympics recognition and reward agreement."
Howard Collins, LU's chief operating officer, said: "We reached agreement with all four unions at the end of May on how we can fairly reward our staff and operate services during the London 2012 Games. Since then we've been working to ensure that the Tube will have the required level of staffing to run enhanced services during the Games.
"We have written to the RMT leadership to provide the reassurance necessary that our agreement is being implemented as intended, and that all staff working in LU stations will have had full and detailed safety training to work alongside qualified supervisors and managers.
"The fact that four-fifths of those balloted chose not to vote or voted 'no' to industrial action shows that we have the support of our staff.
"I know they are keen to play their part in the Games and, now that we have agreement across the board, we can all look forward to focusing on supporting a fantastic summer of sport and cultural events in London."