The president of the association to protect the rights of transportation workers, Mr. Sok Sambath, said there are policemen in front of his office on Wednesday.
He called it's an act of intimidation.
A Phnom Penh police official said he was not aware of police's presence in front of the office of the association but promised to look into it.
The association plans to hold a protest against the rising price of gasoline on August 20th.
Mr. Sok Sambath, said the protest will be carried out as planned although the Phnom Penh city hall has refused to issue a permit.
Phnom Penh authority said it worries about the safety issues and has decided not to issue the permit to protest.