Among the workers readying to march for Indonesia's first Labour Day national holiday are women who used to earn less than $1 an hour making adidas shoes, until they were sacked.
In 2012, about 1300 workers from the Panarub Dwikarya factory spoke up about their working conditions.
Campaigners claimed they were working 65-hour weeks for as little as 5000 rupiah ($A0.46) an hour.
In response, the factory offered "voluntary resignation" with severance pay of 1.6 million rupiah.
But the workers' union says those who refused the offer still lost their jobs and received no severance pay.
The affected staff, all women, still protest weekly outside the factory at Tangerang, west of Jakarta, for their promised entitlements.
Union representative Kokom says Labour Day also takes on significance for the workers who remain at Panarub.
"In January, there were 79 workers here, but since February, it became 68 people with the same target, which is 180 shoes per hour," she told AAP.
"It is too much pressure."
Indonesia's cheap labour makes it an increasingly popular destination for manufacturing, and this has corresponded with an upsurge in union activism.
Last year, President Susilo Bambang Yudhoyono decreed May 1 a holiday from 2014.
Confederation of Indonesian Workers Unions chairman Said Iqbal expects 500,000 workers will march on Thursday.
In Jakarta, they will meet at the palace with 10 demands for the next president, to be elected in July.
At the top is a 30 per cent increase in the minimum wage, which in Jakarta is about 2.4 million rupiah.
"It's very meaningful to make it a national holiday because it's state acknowledgement of labour, even if it's only symbolic," he said.
"This is the moment for us to voice our struggle."
Panarub and adidas did not respond to requests for comment.
Adidas responded to the 2012 strike by urging the factory to pay workers their entitlements, and vowed to stop orders until the dispute was resolved.
