BANGKOK (AP) — Thai authorities have escalated their legal battle against the students leading pro-democracy protests, charging 12 of them with violating a harsh law against defaming the monarchy.

News of the charges comes as the Thai capital Bangkok girded for another rally Wednesday as the students push their demands that Prime Minister Prayuth Chan-ocha and his government step down, the constitution be amended to make it more democratic, and the monarchy be reformed to be made more accountable.

Police on Tuesday issued summonses for 12 protest leaders to answer charges of lese majeste, defaming or insulting key members of the royal family. The offense is punishable by up to 15 years imprisonment.

The law is controversial, because anyone — not just royals or authorities — can lodge a complaint, so it had in the past been used as a weapon in political vendettas. But it has not been employed for the past three years, after King Maha Vajiralongkorn informed the government that he did not wish to see its use. The king has not publicly commented on the law since then.

According to the legal aid group Thai Lawyers for Human Rights, the 12 suspects include top protest leaders known for their public criticism of the monarchy.

Many in the student-led protest movement believe the monarchy holds too much power for a constitutional monarchy. But their challenge is fiercely opposed by royalists, who consider the royal institution an untouchable bedrock of national identity.

One of the 12 protest leaders, Parit “Penguin” Chiwarak, posted his response to the summons on Twitter on Tuesday, saying: “I am not afraid anymore. The ceiling (of our demands) is destroyed. Nobody can stop us now.”

The protest movement late Tuesday night announced a change of venue for their latest rally, which was to put a focus on the monarchy. It had earlier announced that it would be held outside the offices of the Crown Property Bureau, which manages the vast fortune controlled by the king.

The target was switched to the head office of the Siam Commercial Bank, a publicly-held company in which the king is the biggest shareholder. The bank’s headquarters are in a different area of Bangkok, far from the district hosting the Crown Property Bureau and other royal and government offices.

The protest movement announced the change of venue was to avoid a confrontation with police and royalist counter demonstrators, which they said they feared could trigger a declaration of martial law or a coup by the military.

Barbed wire had already been installed around the Crown Property Bureau offices and the government had declared an exclusion zone of 150 meters (500 feet) around the property into which it would be illegal for protesters to enter. The bank, as a commercial enterprise rather than a royal office, apparently would not fall into the legal category of areas where an exclusion zone could be declared.

A protest rally on Nov. 17 turned chaotic, as police employed water cannons and tear gas to block the protesters from entering the Parliament grounds. At least 55 people were hurt, including six reported to have had gunshot wounds, incurred in circumstances that remain unclear. Police denied firing live rounds or rubber bullets.

The next day, several thousand demonstrators gathered outside the national headquarters of the police in central Bangkok to protest the use of force.

The rally at police headquarters was nonviolent but fueled royalist outrage at the protest movement, as demonstrators defaced the Royal Thai Police sign and scrawled graffiti and chanted slogans that could be considered derogatory to the king.

Prayuth reacted by declaring that the protesters had gone too far and could now expect to be prosecuted for their illegal actions. While protest leaders have faced dozens of charges over the past few months, they have generally been freed on bail, and none have yet come to trial.

A statement issued Wednesday by Free Youth, a driving force in a coalition of protest groups, called Thailand a failed state whose people “are ruled by capitalists, military, and feudalists.”

“And under this state, the ruling class oppress the people who are the true founders and heirs of this country,” said the statement, the most strident issued so far in the name of the group.

Many of their rallies have had a light-hearted element, with clever slogans and songs. But the statement declared that “This is not a frivolous fad, it is a fearless fight to light up the future in our generation.”