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 on 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. But the target was later switched to the head office of the Siam Commercial Bank, a publicly-held company in which the king is the biggest shareholder.

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.

The last major rally, outside Parliament, saw chaos and violence as police employed water cannons and tear gas to block the protesters from entering the Parliamentary compound.