Opponents of Srettha Thavisin say the prime minister could face serious legal problems after apparently referring to his party MPs' influences on police promotion - problems that could even include removal from the premiership.

On Thursday petitioner Srisuwan Janya said he would ask the National Anti-Corruption Commission to launch a probe into Mr Srettha's speech during a meeting of Pheu Thai Party MPs on Tuesday.

Recent reports claimed he told the MPs that some of them had successfully pushed for the appointment of new police station chiefs while others were unsuccessful.

The speech violates the constitution, which prohibits MPs and senators from influencing the promotion or transfer of any government official, Mr Srisuwan said.

Wiroj Lakkhanaadisorn from the Move Forward Party said the recent speech amounted to a confession, and it was not difficult to identify the new police station chiefs who received the support and the politicians who gave it.

Prime Minister Srettha said that some had misunderstood the speech.

Somchai Srisutthiyakorn, former election commissioner, wrote on Facebook that the prime minister could be held responsible for violating several sections of the constitution.

On Thursday Mr Srettha reiterated that he never interfered with the promotion or transfer of any police officer.

Deputy Prime Minister Somsak Thepsuthin was tight-lipped when reporters asked him to comment on Mr Srettha's controversial speech.