The typical unionist is now more likely to be a teacher, nurse or childcare worker than to wear a hard hat.

Associate Professor Rae Cooper, a women's employment specialist at the University of Sydney's business school, said the latest Australian Bureau of Statistics data showed 17.5 per cent of male workers were in a union, compared with 18.9 per cent of female workers.

The gender gap has been closing gradually. In the early 1990s, women trailed men in union membership by 10 percentage points. By 2000 it was closer to five. "In part, that is a story about the new heartlands for unions, especially the retreat of unions to the public sector," Professor Cooper said.

ACTU president Ged Kearney said unions had become more focused on policies that directly affected women in the workforce.

''We ran a huge campaign last year when the Fair Work Act was being scrutinised to increase the right to request family-friendly work arrangements and that was taken up at the highest level of the union movement," she said.

Ms Kearney said unions were preparing to fight to protect the minimum wage, penalty rates, the award system and collective bargaining, which affected mostly female workers.

Dr Cooper said the equal pay case run by the Australian Services Union was a ''great victory'' for women members. ''Increasingly, smart people in unions are looking at pay parity, gender equity audits and pushing an agenda of assisting women to build meaningful careers,'' she said.

Professor John Buchanan, director of the Workplace Research Centre at the University of Sydney, said about 30 per cent of unionists now worked in a school, hospital or supermarket.

''The way the government is constructing the IR debate, you'd think all unionists were construction workers and miners,'' he said. ''They are a tiny proportion of the workforce and the union movement faces deep changes.

"[Unions are] not just taking up new conditions such as paid parental leave, they are also looking at improving wages for people in childcare and early childhood education."

Morgyn McCarthy Harding, 25, has been a member of the Ambulance Employees Association Victoria for four years. Members of her union are more likely to be younger women instead of older men, as was the case 10 years ago.

She said the greater involvement of women in the union had softened its image. ''I agree with what unions stand for. I believe in workers' rights and … that everyone is entitled to good conditions and fair pay,'' she said.