BANGKOK, Thailand (AP) — Thai activists hoping to keep up the momentum in their campaign for democratic change launched a third major rally in Bangkok on Wednesday, amid concerns about possible confrontations with police or rival groups supporting the government.

Plans for the rally at Bangkok’s Democracy Monument have been complicated by King Maha Vajiralongkorn’s duties, which include him being driven around the protest venue to attend a royal ceremony.

The protest leaders said they will make way for the king, and police said they are confident they can control the crowds. Still, there is possibility that protesters, widely seen as unsympathetic to the king, could at a minimum show public disrespect for the crown.

The king made a similar drive on Tuesday after police cleared tents set up near the monument and arrested 21 people on minor charges.

While the rally had been scheduled to launch at 2 p.m., organizers issued a post-midnight call for followers to start turning up at 8 a.m. to assure they could secure the venue.

The area was blanketed with police, stationed in an organized manner but wearing yellow shirts instead of standard uniforms. Yellow shirts are a symbol of devotion to the monarchy, and strongly associated with conservative politics.

The protesters have said they plan to march to Government House — the office of Prime Minister Prayuth Chan-ocha — and surround it for at least a night.

“We have to fight,” said university student Kanokwan Kawkaew, 20. “If we don’t fight, we will lose again.”

Historically, attempts to bring democratic reform to Thailand have sooner or later been reversed by military coups.

The crowds at the last two rallies, held on weekends, were significant in number, with the Sept. 19 event estimated to be have attracted at least 20,000 people. But turnout could be weaker this time, which falls on a weekday amid daily rain.

The protesters have drawn attention, and scorn in some quarters, because of their demands for reforms in Thailand’s constitutional monarchy, which they claim does not properly operate in a democratic framework.

That demand has caused a huge controversy, because the royal institution has long been considered sacrosanct and a pillar of Thai identity. It is also protected by a lese majeste law that mandates three to 15 years in prison for defaming the monarchy.

Conservative royalist Thais are suspicious of the protesters, accusing them of seeking to end the monarchy, an allegation they deny. However, the activists publicly identify closely with the 1932 revolution that ended the absolute monarchy.

Several royalist groups announced plans to stage counter-demonstrations near the rally, but their previous efforts gained little popular support.

The turnout of yellow-shirted civilians appeared to be much larger Wednesday. There was speculation that such counter-demonstrators were organized by authorities, as postings on social media showed municipal trucks carrying groups of people all wearing yellow shirts. They could be distinguished from police, who are compelled to wear short back-and-sides haircuts.

The other historical link claimed by Wednesday’s protesters is the date of the rally, which is the anniversary of the 1973 popular uprising that led to the toppling of a military dictatorship.

The protest movement was launched in March by university students but quickly put on hold as Thailand was gripped by surges in coronavirus cases. It came back in July, when the threat from the virus eased, and since then has again been spearheaded by students and publicized on social media.

The movement’s original core demands were new elections, changes in the constitution to make it more democratic, and an end to intimidation of activists.

The protesters charge that Prime Minister Prayuth, who as army commander led a 2014 coup toppling an elected government, was returned to power unfairly in last year’s general election because the laws had been changed to favor a pro-military party. Protesters say a constitution promulgated under military rule is undemocratic.