Sunday’s protest, billed as the “Merry Xmas Mr Prime Minister” march by organisers, was the fourth day of demonstrations in the past week by leftist opposition parties, student groups and civilians campaigning against Mr Orban’s government.
The new law allows employers to ask for up to 400 hours of overtime work per year, leading critics to label it the “slave law”.
Mr Orban’s government has also faced criticism over a recently-passed law allowing the government to establish new administrative courts. The courts will oversee sensitive issues such as electoral law, protests and corruption issues.
Activists waved both Hungarian and EU flags as they marched from Heroes’ Square towards parliament.
“Discontent is growing,” said Andi, 26, a sociology student who attended Sunday’s march. “They have passed two laws this week which ... won’t serve Hungarian people’s interest.”
Mr Orban has repeatedly clashed with EU leaders in Brussels after boosting his control over the courts and the media.
Civil rights watchdogs said the new court law was the latest erosion of democratic institutions under the country’s prime minister, who came to power in 2010.
He has since tweaked the election system to favour his ruling Fidesz party and has put loyalists at the head of public institutions.
He has rarely angered large voter groups, but street demonstrations organised by left-wing groups began in the capital earlier this week. On Thursday police used tear gas on protesters outside the parliament building.
Mr Orban was re-elected in April on the back of a fiercely anti-immigration campaign, facing a weak and fragmented opposition.
Earlier this month, his government forced the Central European University to leave Hungary as part of Mr Orban’s long-running campaign against its founder, the Hungarian-born billionaire George Soros.
Fidesz released a statement on Saturday claiming it was “increasingly obvious that criminals have been part of the street riots organised by the Soros-network".
Additional reporting by Reuters
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