A fight between three mainlanders from a tour group and a Macau guide saw more than 100 of his colleagues take to the street to lay siege to the tourists' coach.
As the row worsened, police made a protective cordon around the bus which had just picked up the tour group from an erotic show at Jai Alai casino late on Monday night.
Officers ended up taking the three alleged attackers to a police station. All three were later released but yesterday a Macau tour guide trade union launched legal proceedings against them.
Wu Wai-fong, president of the Macau Tour Guides Association, said it was the only way to protect tour guides in Macau from being harassed in the future.
'We have to send a strong signal to the tourists that they cannot attack us,' Wu said.
He blamed trouble between mainland tourists and their guides in Hong Kong for fuelling the problem.
'Tourists are rude and cases in Hong Kong worsen the situation,' he said. 'The tourists think they can receive compensation if they can make us angry and hit back. If we are not taking action now, our tour guides will receive no protection in the future.'
The trouble started at the Macau ferry terminal when tourists claimed their tour guide was late. Another guide tried to calm the situation but was allegedly turned on by the three tourists instead.
The tour group, including the three alleged attackers, left Macau to return to Liaoning province early yesterday.
'The tour guides are very worried, therefore they carried out a united action on Monday evening,' Wu said.
The association understood it would be difficult to summon the men back to Macau, but action needed to be taken to deter future violence against its members, Wu said.
Hong Kong and Macau are popular destinations for mainland tourists, who have to go through complicated visa applications for trips abroad.
The appreciation of the yuan also makes shopping in Hong Kong and Macau good value for money.
But the cheap cost of some tours has led to mainland tourists complaining that they are being forced to shop in designated shops where the guides earn commission.
Macau's prosecution department has asked the Customs Service to investigate the case. The Customs Service, meanwhile, said that it had no legal grounds for preventing the alleged attackers from leaving Macau yesterday because legal proceedings had not yet began.