Staff in Transport for London's travel information and call centres will walk out for 24 hours in a dispute over a bonus for the Olympics, a union said.
The Rail, Maritime and Transport (RMT) union said its members will go on strike from 21:30 BST on 1 July.
Staff were not permitted to volunteer as 2012 travel ambassadors and some are banned from taking leave, the RMT said.
TfL said the action was "unjustified" as 14% of the 212 non-frontline staff balloted by the union voted to strike.
The union said TfL had refused to meet at the conciliation service Acas to resolve the dispute.