Prime Minister Somchai Wongsawat has fired the chief of Thailand's national police force.
No official reason was given for his demotion which came amid mounting tension over protests paralysing Bangkok's two airports.
Police have now ordered protesters to quit the smaller Don Mueang airport. Riot police are reported to be in place at the international airport.
Anti-government protesters say they will not leave until Mr Somchai resigns, which he has refused to do.
Police have not yet moved to break up the protests but said earlier they were prepared to take "other steps" if negotiations failed.
A government spokesman said on Thai TV on Friday that the prime minister had appointed Major General Prateep Tanprasert as acting police chief.
The BBC reports that rumours of a coup are circling in the capital.
Earlier this week, army chief, General Anupong Paochinda, urged Mr Somchai to call a snap election as a way of easing the crisis.
Thousands of passengers are stranded in Bangkok by the crisis.
Thailand has been in political turmoil since former Prime Minister Thaksin Shinawatra was ousted in a military coup in 2006.
The People's League for Democracy - a loose alliance of royalists, businessmen and the urban middle class - claims that the government is corrupt and hostile to the monarchy.
They have occupied a government complex in Bangkok for months, and declared at the beginning of this week that they were embarking on the "final battle" of their campaign to unseat the government.