About 1,000 workers gathered at Government House on Sunday, calling on the government to end unfair contracts and unsafe working conditions in both the private and public sectors.
The workers, led by labour rights advocates Sawit Kaewwan and Chalee Loysoong, marched from the Democracy Monument to Government House to raise awareness about the treatment of workers to mark the "World Day for Decent Work 2018" on Sunday.
They dispersed after handing in a petition demanding the government ensure decent wages, and safe and secure jobs to the government's representative.
The petition was accepted by Kittipong Laoniphon, deputy director-general of the Department of Labour Protection and Welfare.
Mr Sawit, president of the Thai Labour Solidarity Committee (TLSC), said unfair contracts are rampant and those working in the government sector are not spared.
He said some government agencies, such as the Public Health Ministry and the Social Security Office (SSO), no longer accept civil servants as permanent staff, and their new recruits are hired as contract workers with different terms of employment.
Mr Sawit said the government should enact a bill on forced labour, and groups will keep a close watch on the issue.
The bill on forced labour is essential after Thailand ratified the Protocol to the Forced Labour Convention in June, which requires Thailand to promulgate a related law within one year.
Mr Chalee, vice-president of TLSC, said job security is being taken away and wages pushed down as a result of sub-contracting and the ratio of subcontracted workers and full time employees currently stands at 60:40.
Sub-contractors lack job security and are deprived of welfare benefits, he said, adding their calls have fallen on deaf ears for past three years.
He added that the SSO's preference of four-year renewable contracts over long-term hires is unfair and should end.
Mr Chalee said safe working conditions are also compromised, as reflected by the increase in compensation claims for illness and injuries by the workers.
Osot Suwansawet, president of the Union for State Employees, said the group, which comprises mostly health care personnel, will step up calls for decent pay and benefits.
He said the group has raised the issue with the Public Health Ministry and is prepared to renew its demands. No response was to hand from the ministry on why it prefers temps and sub-contracting.
There are more than 500,000 non-civil servant state employees with around 140,000 temporary staff at the the Public Health Ministry alone who have complained about inequality in pay and benefits.
The proposed forced labour prevention law is designed to address the problem, but even labour experts agree that it lacks measures to protect employees.