The People's Democratic Reform Committee on Monday filed a lawsuit with the Civil Court asking it to order the revocation of the emergency decree, conduct an urgent investigation and issue an injunction to prevent a crackdown on protesters.
The lawsuit was filed by Thaworn Senneam, a PDRC leader at the Victory Monument rally site, and his lawyers.
Named defendants in the lawsuit are caretaker Prime Minister Yingluck Shinawatra, caretaker Labour Minister Chalerm Yubamrung, director of the Centre for Maintaining Peace and Order (CMPO), and Pol Gen Adul Saengsingkaew, the national police chief and CMPO chief of operations.
Mr Thaworn, while waiting for the court's decision, said the government's imposition of the emergency decree was illegal because the Constitution Court had earlier ruled that the PDRC protest was legal.
There had been violence against the protesters, the most recent being the fatal shooting of Sutin Tharatin, coordinator of the People's Democratic Force to Overthrow Thaksinism, near an advance voting unit in Bang Na area on Sunday.
The violence had not been caused by the PDRC protesters, but by other people, Mr Thaworn said.
In PDRC's view, the emergency decree was designed to give the authorities the power to curtail the people's basic rights, he added.