Cleaners at John Lewis Partnership are to ballot on strike action at the firm's flagship Oxford Street store in London.
The 33 cleaners are in dispute with sub-contractor Integrated Cleaning Management over pay.
They want the London living wage - £8.55 an hour. Currently they are paid just £6.72 an hour, little more than the minimum wage.
The cleaners are members of the Industrial Workers of Great Britain union.
John Lewis made profits of over £400 million last year. It pays bonuses to its employees but the cleaners are excluded because they work for a sub-contractor.
Labour MP John McDonnell said: "There is now a new alliance being put together in terms of trade unions supporting the London living wage campaign because people cannot take it anymore."
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