Thai lawmakers Thursday failed to reach an agreement on a pathway to amend the constitution, further angering anti-government demonstrators calling for more democracy and reform of the monarchy.

The parliament overwhelmingly backed a proposal to set up a panel to study various plans to amend the charter written by a military-appointed panel after a 2014 coup. The vote, mostly backed by the key ruling party and the Senate, means the process for rewriting the constitution will be pushed back by at least one month. Opposition parties said they won’t join the panel mooted by the government.

Hundreds of agitated demonstrators, who had gathered outside the parliament, tried to stop vehicles of some senators and lawmakers leaving the house after the decision. The protesters have been hitting the streets since July to demand changes that include scrapping the military-appointed senate — which played a key role in the return of coup leader Prayut Chan-ocha as prime minister after the election last year — and reining in the power of King Maha Vajiralongkorn.