Margaret Prosser, of the TUC's ruling General Council, said that part- time work was often carried out in a twilight world of private nursing homes and "seedy sweatshops".
Ms Prosser, national officer of the Transport and General Workers' Union, said that defending the rights of the country's six million part-time workers was the key to the union movement's future.
Introducing a General Council statement on the issue, she said the TUC would campaign to introduce a national minimum wage of pounds 4.15 for all workers, not just full-time employees.
Since the abolition of wages councils in 1993, the pay of part-timers, the majority of whom are women, has been hit hard, she said.
The poorest of them have suffered a real cut in their pay of 4p from every pound they earn. Tory claims that the wages of part-time employees were rising faster than full-timers were "codswallop". The gap between those with full-time jobs and those with part-time jobs was growing, she said.
Ministers insist that many people want to work part-time. For some, it is an attractive option, but for others it is the only way to combine the need to earn an income and cope with the demands of family life. A growing number of people were simply unable to find full-time work, Ms Prosser said.
Nearly a million people were forced to juggle two or more jobs in order to earn a living.
Many of them were "terrified to speak out and join a union for fear of the sack". The union movement should be the natural home for these workers.
"At the start of this century a wave of new unionism was born from the struggles of the poor, the unskilled and casual workers - the very people who, up until that point, were seen as beyond the reach of trade unionism," she said.
"As the next millennium approaches, I hope we will see a second wave of new unionism. And that part-time and women workers will be at its fore."
tMs Prosser is set to take over as the next president of the TUC. Margaret Prosser, 58, national organiser of the Transport and General Workers' Union, will take over the prestigious role from finance union chief Leif Mills at the end of the TUC conference on Friday.
Ms Prosser chairs the TUC women's committee and last week attended the UN women's conference in Beijing.
Tony Dubbins, general secretary of the Graphical Paper and Media Union, had been due to become president but decided to postpone his appointment for a year following the recent death of his wife.
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