Thai lawmakers moved to change parts of the country's military-backed constitution after its highest court agreed to hear a case that may block them from doing so, signaling a renewed round of political tension.

Parliamentarians took an initial step early Thursday to approve three bills that would establish a fully elected Senate and make it harder for the courts to disband political parties. The Constitutional Court on Wednesday accepted a petition from an appointed senator seeking to block some of the amendments.

The battle is the latest between allies of former Prime Minister Thaksin Shinawatra who have won the past five elections, and royalists who backed his ouster in a 2006 coup. Street protests since then have killed more than 100 people and led to takeovers of the airports and central business district.