More than 10,000 motorised tricycle drivers rallied near the Xian municipal government office in Shaanxi province against a ban forcing three-wheelers from the streets, protesters said.
Police sent 400 officers to the scene of the rally, held on Monday, and took away at least four representatives, a protester surnamed Gui said yesterday.
'We have more than 30,000 drivers in the city demanding the right to ply our trade,' said Mr Gui, a 36-year-old army veteran.
He said the drivers were planing a bigger demonstration today. All of their representatives were released yesterday. 'We will continue our protest until the related authorities solve our problem,' he said.
Some of those involved in Monday's demonstration carried banners reading, 'We don't steal, we don't rob, we don't fight, so why is our livelihood against the law?' Others read, 'Government, have mercy on miserable laid-off workers - we must eat'.
Protesters said the government had ordered a media blackout, with city television stations and newspapers not reporting the unrest.