Cleaners who work for major financial firms at London's Canary Wharf are continuing a campaign to put an end to what they describe as "poverty" wages.
Some firms were presented with a golden vacuum cleaner
Members of the Transport and General Workers Union (T&G) are demonstrating outside offices of businesses who use cleaning contractor ISS.
The union, which is demanding a pay rise for cleaners, claims workers often receive no sick or holiday pay.
ISS said it is in talks with the T&G and was disappointed by the protest.
From Wednesday until Friday workers will target the offices of Goldman Sachs, PriceWaterHouseCooper, Nomura, Linklaters, Lovells, Marsh Ltd and CitiGroup.
According to the union, cleaners receive different wages from building to building for doing the same job.
It also claims many earn £5.35 per hour despite the high living costs in London.
General secretary of the T&G Tony Woodley said firms that "suck cleaners dry" will get a so-called golden vacuum cleaner.
"The City fat cats are living the high life whilst cleaners are scraping by on poverty wages, he said.
"It is obscene and unjust, and makes a mockery of the claims of big business that they exercise any corporate social responsibility."
An ISS spokesman said: "We are currently in discussions with senior TGWU officials in connection with collective bargaining arrangements in London, so we are extremely disappointed at the demonstrations the TGWU has called.
"We have had good relations with the union in the past and we are committed to continuing discussions towards agreement."