Opposition activists from across Cambodia are expected to descend on Phnom Penh today, bringing a petition for CNRP lawmakers to deliver to the King, even as the National Assembly’s permanent committee determines whether to allow a criminal case against the party’s acting president, Kem Sokha, to proceed.

In what one opposition source called “drawing a line in the sand”, the elected representatives and supporters will gather at the party’s Phnom Penh headquarters before lawmakers take the petition to King Norodom Sihamoni, asking the monarch to intervene and stop what’s been widely labelled a political crackdown against the party and government critics.

“We will see in black and white tomorrow the National Assembly’s decision,” Cambodia National Rescue Party lawmaker Eng Chhay Eang said yesterday. He called for “all compatriots” to take note of the plans and added that opposition lawmakers would sit out the session.

“We don’t know what the situation will become … we cannot go to sit in the National Assembly to watch [the CPP lawmakers] bash our heads, so we will not join.”

The action coincides with the fourth week of the “Black Monday” campaign, in which activists wear black clothing to protest the imprisonment of five people – all current or former human rights workers – for a supposed conspiracy to cover-up an affair by Sokha.

Reports from opposition sources yesterday differed as to how the petition would be delivered to the palace and whether a procession would be led through the streets.

Yesterday evening, CNRP lawmaker Ho Vann said most lawmakers would arrive in cars but said people could follow.

“There might be people following us by motorbike,” Vann said, adding that parliamentarians would also be at the National Assembly to accept petitions from supporters, too.

Amid the rising tensions – which one observer called “very dangerous” – representatives of both City Hall and the gendarmerie yesterday vowed to maintain order.

Having characterised “Black Monday” as a “colour revolution” intended to topple the government, authorities have declared unauthorised protests illegal, while several opposition supporters have been detained while collecting thumbprints for the petition.

Deputy City Governor Khuong Sreng yesterday said that without permission, any march by the CNRP would be blocked. “Doing it legally is OK; doing it illegally – no way,” he said.

But as the weight of questionable legal cases continues to mount on the party, an opposition member yesterday said he wanted lawmakers to take to the streets, declaring “enough is enough”.

“Tomorrow is a proactive offensive move; we want to test the government. Will they back down or take us out?” the source, who requested anonymity, said. “Before, we were still talking, making deals, but Hun Sen is not to be trusted, he cannot do this . . . We need to draw a line in the sand. Everyone might get arrested.”

At the assembly this morning, the lawmakers from the ruling Cambodian People’s Party will vote on whether to disregard Sokha’s parliamentary immunity and allow a criminal case against him to proceed.

Sokha was provisionally charged for ignoring a court summons on Thursday. The hearing was related to accusations he – with the help of two fellow opposition lawmakers – procured a prostitute.

News of the charge emerged following an attempt by armed police to arrest the opposition leader at CNRP headquarters, where lawmakers, and a throng of supporters, are now maintaining a 24-hour presence.

Authorities hold that Sokha’s offence constitutes a flagrant crime, thus allowing them to ignore his immunity. The CNRP and observers, however, say the CPP, employing Sokha’s alleged affair as pretext, is using its control of the judicial system to neutralise their political opponents ahead of coming elections.

Amid the public backlash, the Ministry of Justice on Saturday announced a special training to “educate” journalists about the penal code.

The CNRP has called for National Assembly President Heng Samrin to block today’s vote, which they say breaches the constitution. A letter to this effect will also be delivered to the parliament today.

However, CPP lawmaker and National Assembly spokesman Chheang Vun said the parliament was merely following procedure after being informed of the charge against Sokha.

Though it takes a two-thirds majority vote to strip parliamentary immunity, this was irrelevant in Sokha’s case because he had committed a flagrant crime, Vun argued, before summing up the essence of the vote. “Do we let the court [pursue the case] more or not?” Vun said.

The CNRP and a major trade union have said they will stage a mass demonstration if Sokha is arrested.

Speaking on condition of anonymity, a political observer said he was concerned about what today’s action might lead to, and added authorities would likely block activists in their provinces and cordon off the area around CNRP headquarters to contain the protest.

“This is very dangerous, because the opposition party seems to have run out of real options to fight back and protect Kem Sokha,” they said.

“And it is not just about Kem Sokha . . . If they are desperate enough to do this, it’s because they do not have any other way to protect themselves.”

Speaking yesterday, National Military Police spokesman Eng Hy would not discuss if extra measures would be taken, only to say the body would “monitor” the group. “It is our military’s role to safeguard security and social order for the nation,” he said.