London commuters and holiday shoppers could face a Tube strike over the Christmas period, as union members consider a walk out.

Underground cleaners from the Rail, Maritime and Transport Workers (RMT) union started voting on a possible strike yesterday.

Action could take place in December and cause “significant disruption” according to a union boss, City AM has reported.

Cleaning staff do not receive the same pensions, sick pay and free travel as other Transport for London (TfL) workers on the Underground, because they are employed by American-based contractor ABM.

Union members are now considering striking for better conditions, and an increase to their £19,029 annual salary.

Some 1,000 Tube cleaners – around half the total number – are signed up to the union.

RMT General Secretary Mick Cash said: “It is scandalous that the people who do some of the hardest and dirtiest work on London’s transport network are treated differently to other London Underground staff while the company that employs them and its top executives profit from their work.

“The disgrace of the two-tier workforce on London Underground is a stain on the capital city and RMT intends to make support for this essential group of workers, keeping London moving day in and day out, a major election issue.”

An ABM spokesperson said the company was “disappointed” that RMT was balloting for a strike.

She said: “Our colleagues are the best in the business and play a vital role in keeping the London Underground clean, all year round.

“For that reason, we are pleased to offer a pay and benefits package that compares favourably to the average for the cleaning profession in the UK.”

She added: “A strike threatens unnecessary disruption and delay for the millions of customers that rely on the Tube every day.”