Drivers in three provinces express indignation over a directive to enforce the Land Traffic Law.
Police and demonstrators clashed in Siem Reap on Monday over efforts by authorities to collect motor taxes.
Vor Vorn, 31, a resident of Siem Reap who claimed to represent the protesters there, said about 3,000 people had intended to demonstrate along the city's central thoroughfare Pub Street, but that police had prevented many from participating.
"Police blocked the street so we could not get through on our motorbikes," he said. "Several of us tried to crash through the barricades, but the police came and fought with us."
Vor Vorn added that there were no injuries and no arrests made during the rioting in Siem Reap.
"We did not want to make trouble for the police. We just wanted to send a message to the government to reduce the cost of motor taxes," Vor Vorn said.
We just wanted to send a message ... to reduce the cost of motor taxes.
The demonstrations followed a directive issued earlier this month by Prime Minister Hun Sen ordering provincial police across the Kingdom to collect motor taxes in accordance with Cambodia's Land Traffic Law.
You Vala, who participated in the protests in Siem Reap, said many drivers own cheap, illegally imported motorbikes because they can't afford legal ones, and that they were uncertain about how much they would be required to pay to properly license their motorbikes.
"If we were rich, we would have purchased proper motorbikes," You Vala said, adding that authorities should blame themselves for not cracking down sooner on those who import motorbikes without paying the necessary taxes.
Siem Reap Governor Sou Phirin was unavailable for comment on Monday, as were provincial customs officials.
Under Article 79 of the Land Traffic Law, driving a vehicle without a licence plate incurs a fine of between 25,000 riels and 200,000 riels ($6 and $48).
Demonstrations were also reported in Svay Rieng and Banteay Meanchey, where residents reported that two protesters were briefly detained.
"About a thousand people gathered [in Banteay Meanchey] with their motorbikes and burned tyres to protest the taxes," said local resident Thun Sophea.