Thailand's state anti-corruption body has ruled that 308 pro-government lawmakers acted illegally in seeking to pass a bill to make Parliament's upper house an all-elected body.

Tuesday's ruling by the National Anti-Corruption Commission will lead to a further investigation, and could eventually result in the lawmakers being banned from politics.

Prime Minister Yingluck Shinawatra was not included among those found to have acted improperly. She dissolved Parliament in early December and called new polls for Feb. 2.

The commission did not explain its ruling. The Constitutional Court earlier ruled that the lawmakers acted illegally by violating legislative procedures and weakening the system of administrative checks and balances.

Protesters are demanding that no election be held until an appointed government institutes political reforms. The opposition Democrat Party is boycotting the polls.