Embattled Malaysian Prime Minister Najib Razak may face another political challenge when critics of his government stage a potentially massive rally this weekend to demand his resignation. The rally, also known as "Bersih 4", will be held in Kuala Lumpur, Sabah and Sarawak tomorrow and on Sunday, just ahead of the country's Independence Day on Monday. Malaysian police have said the event is unlawful and called on the public to stay away, setting the stage for clashes between participants and officers. Organiser Maria Chin Abdullah on Wednesday said the rally would not interrupt official celebrations for Independence Day, also known as Merdeka, and that the demonstration was the people's way of celebrating the occasion. "We will not disturb it because we still respect Merdeka Day but they have to also recognise that Bersih 4 is part and parcel of National Day, and it is the people's way of celebrating it in calling for change and reform at a national level," Chin told The Malay Mail Online . A large crowd has already gathered at the city square of Batu Pahat, a town in the Northeast of Johor state as of Wednesday. According to The Star , protesters, mostly wearing yellow T-shirts, chanted slogans such as "Bersih" - which means clean in Malay - and sang the national anthem. As Najib's government attempts to contain the financial scandal surrounding state investment fund 1MDB, some analysts have said this weekend's event is likely to draw a smaller crowd than the last Bersih rally, blaming a divided opposition coalition. A record 300,000 protesters turned up at the 2012 rally, which later turned violent as police used tear gas and water canons. But Oh Ei Sun, a senior fellow with the S. Rajaratnam School of International Studies, Nanyang Technological University, said Bersih 4 would still draw a big crowd as many from the country's middle class have been "irked by the series of scandals". He added that the prospect of change would depend on the crowd's composition rather than its size. "For example, if Dr Mahathir [Mohamad] joins the rally, or there are many Malays or [ruling party] UMNO participants, then the political pressure on Najib will pile on a bit," Oh said. The Malaysian prime minister has been under mounting pressure to resign over allegations surrounding the corrupt-tion and mismanagement of 1MDB, a state-owned invest-ment fund whose advisory board is headed by Najib. Last week, Najib wrote on his Facebook that no one should attempt to "interfere with or hijack" his obligation to lead the country. Speaking ahead of the rally, opposition leader Lim Guan Eng said in Hong Kong that the financial scandal had not only prompted ordinary Malaysians to question Najib's integrity but also set the stage for political realignment in the country. The head of Malaysia's biggest opposition party, Democratic Action Party (DAP), said the situation in Malaysia is so grim that he is willing to sit down with former prime minister Mahathir, the man who sent him to prison twice, to discuss ways to remove Najib from power. "Malaysia is marching backward, not moving forward, so I prefer to keep an open mind to having discussion with Tun Dr Mahathir," Lim said. While the former opposition coalition has been "split asunder", Lim said this could be a blessing in disguise as it has given rise to a new moderate and progressive Islamic movement called the New Hope Movement.