Greek riot police have fired tear gas to break up a protest by hundreds of fellow officers.
A wave of industrial unrest has swept the country
The clash happened as the protesters marched on the finance ministry in the capital, Athens, demanding they be paid proper allowances in recognition of the hazardous nature of their work.
Marching with hundreds of firemen and members of the port authorities, the policemen swept into the entrance of the ministry where they staged a sit-in.
The demonstration marks a further escalation of the industrial unrest which has swept the country since the beginning of the month, in which doctors, teachers, university lecturers and other state employees have all gone on strike over pay.
When the police protesters refused to move from the ministry, riot police fired off rounds of tear gas and chased them through the streets.
The protesters vowed to continue the blockade to stop civil servants going to work on Thursday.
They had earlier been fired up by the president of the policemen's union, who accused the government of fooling them by continually promising pay rises and then giving nothing.
A member of the port authorities said they had had enough.
"All the other workers here in Greece are making good salaries," he said.
"But because we cannot go on strike - it's prohibited for us to strike - they don't give us enough money.
"Eight hundred euros a month is not enough money for a family here in Greece."
There was further bad news for the government on Wednesday, when doctors at state hospitals in the Athens area decided to continue their strike which began earlier this week.
Taxi drivers also began another 48-hour stoppage and next week many of the most important tourist sites will again be closed due to industrial action.
All those on strike are demanding better pay and conditions.