In Sa Kaew, police stopped a bus with 50 members of an anti-government group at a checkpoint on Suwannasorn Road in the province's Muang district for two hours.

They did not allow the bus to proceed until the 50 protesters disembarked and blocked the road.

A retired schoolteacher on the bus said it had earlier been stopped at four checkpoints for about 30 minutes each time.

Protesters travelling from Khon Kaen had to switch from a chartered bus to a six-wheel truck and then to passenger sedans, after police cited traffic regulations to prevent them from using the first two vehicles, said Somyong Kaewsunthorn.

Somyong is the head a national group opposing the government's school transfer policy and a deputy leader of an anti-government network. An unusually large number of checkpoints had been set up along Bangkok-bound lanes of Phetkasem Road in Phetchaburi.

Buses were stopped and drivers asked about their destinations.

The chairman of the Law Society of Thailand's human rights committee said criminal complaints could be filed against any officers who tried to prevent anyone from joining the rally.

Somchai Homla-or also said the officers could be charged with violating Constitutional rights.

Somchai said a petition could be filed with the Supreme Administra-tive Court asking that any order from the police executive command level to block protesters be nullified.

Complaints involving such cases can be made to the Law Society by calling 02 282-9906.