Loos and classrooms in six of the London borough’s schools will be left in a mess if the ballot, which closes on Monday December 18, results in a vote to strike, their union Unite warned.
The ballot was launched after employers OCS Group Ltd refused to grant holiday pay in line with its legal obligations, Unite said.
Bosses also refused to discuss a 5 per cent pay claim for April next year and their imposition of term-time-only contracts, according to the union.
Unite regional officer Onay Kasab said: “What we have here is outrageous salami-slicing by OCS of pay and employment conditions of an already lowly paid group of workers.
“OCS, which is a very poor example of the privatised contracting-out culture, has cut pay for the cleaners and refuses to uprate the London living wage to the current rate of £10.20 an hour.”
OCS Group did not respond to requests for comment.