The typical unionist no longer wears a hard hat but is more likely to be a teacher, a nurse or childcare worker, workplace experts say.

Almost 19 per cent of female workers are members of a union, compared with 17.5 per cent of male workers. In 1990, 35 per cent of women and 45 per cent of men and were in unions, Australian Bureau of Statistics figures show.

As a result of the change, greater job flexibility, family-friendly hours, equal pay, paid parental leave and domestic violence leave dominate the union agenda. Ged Kearney, a former nurse and now president of the Australian Council of Trade Unions, said unions were more focused on policies that directly affect women.

''We ran a huge campaign last year … 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 would fight to protect the minimum wage, penalty rates, the award system and collective bargaining, which mostly affect women workers, who comprise a big proportion of workers in low-paid jobs.

''The impact of getting rid of all those basic protections that we have in the Fair Work Act will severely impact on women, and this has made our resolve even greater now to pursue these advancements for working women,'' she said.

Sydney University business school associate professor Rae Cooper said unions were now strongest in the public sector.

''In part, that is a story about the new heartlands for unions, especially the retreat of unions to the public sector," she said.

She cited the equal-pay case run by the Australian Services Union in 2012 as a ''great victory'' for the mostly female social and other community workers it represents.

''Increasingly, smart people in unions are looking at pay parity, gender equity audits, and pushing along an agenda of assisting women to build meaningful careers,'' she said.

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

''The way the government is constructing the IR [industrial relations] debate, you'd think all unionists were construction workers and miners,'' Professor Buchanan said.

''They are a tiny proportion of the workforce and the union movement faces deep changes. Issues associated with caring responsibilities are now at the centre of the agenda for many unions.''

Marian Rakosi, 24, an early childhood teacher in Kingsford, joined United Voice to campaign for better professional recognition and higher wages.

She and her colleagues have been ''ridiculously underpaid and under valued'', she said.

Like teachers with students and nurses with patients, Ms Rakosi said she had a role to advocate for quality early education.

''For me, unions are about getting people together who have the same issue and who want to fight for social justice and equality in our world," Ms Rakosi said.