Thousands of protesters marched through the streets of Sydney's CBD today, waving colourful banners and chanting demands for equal pay for women.

The Australian Services Union, which represents workers in the female-dominated community services sector, organised the nationwide rally - Australia's biggest equal pay march since the 1970s.

Women earn 18 per cent less than men, which amounts to about $1 million over a lifetime, recent Australian Bureau of Statistics show.

But the union's NSW secretary Sally McManus said the pay gap could be as high as 35 per cent in the community sector.