The GMB union said 900 of its members employed by the City of London Corporation will walk out on May 25 at attractions including Tower Bridge, the Barbican, museums, gardens, parks and markets after voting overwhelmingly in favour of industrial action.
Anna Lee, GMB London region organiser, said: "This vote and support for strike action confirms how strongly our members feel and how this cost-of-living crisis is having such a devastating impact on them and their families.
“This 'them and us' culture within the Corporation of London has to end.
“It is not OK for workers to be using food banks whilst corporation bosses spend thousands of pounds of taxpayers' money on hospitality - while telling staff there's no money for pay.
“Our members do not take this action lightly, but our demands for fair pay have been falling on deaf ears for months.
“No one wants to go on strike but our members feel they are not being listened to, now they feel they have no alternative.
“GMB calls on the City of London Corporation to properly value and respect their staff and return to the negotiating table."