Malaysian police raided the office of the Bersih 2.0 Yellow Shirt movement ahead of the planned anti-Najib rally on Saturday.
The law enforcement agencies sad the raid was in line with a law prohibiting acts undermining parliamentary democracy, the Malay Mail reported.
Mandeep Singh, a leader of the Bersih 2.0 movement, said the office in Petaling Jaya was raided and the police took possession of the belongings and documents.
"Bukit Aman in our office. Want to 'rampas' (confiscate) all our 'barang' (things)," he tweeted.
Saturday's rally against the government is the toughest challenge Prime Minister Najib Razak has faced in recent times. Opposition patriarch Mahathir Mohamad has also asked Malaysians to join the massive anti-government rally on Saturday. A defiant Najib has said street protests cannot unseat him, referring to the Bersih 5 or 'Yellow Shirt' demonstration seeking his government's ouster.
Kuala Lumpur is preparing to deal with clashes on Saturday as outfits supporting Najib and his government under the 'Red Shirts' umbrella have pledged to come out into the streets to confront the Yellow Shirts.
With both the Yellow Shirts and the Red Shirts organizing protests in the Dataran Merdeka in the heart of Kuala Lumpur, the city will be under lockdown on Saturday. The Red Shirts say the Bersih is trying to remove a legally elected government and that the opposition is serving 'foreign agenda'.
Former prime minister Mahathir said Malaysians should show dissatisfaction with the Government by taking part in this demonstration by Bersih in Dataran Merdeka.
"Malaysia is now in distress because (Prime Minister) Datuk Seri Najib's administration has caused the country to rake up billions of ringgit in debts that are unable to be paid by the Government and the country," Mahathir said.
In September the police accused Bersih 2.0 chairman Maria Chin Abdullah of trying to topple the government.
Rally details on Saturday
Meanwhile, the organizers have given out the details of rally on Saturday. The rally participants will gather in two places On 19 November 2016 - Bangsar LRT (Dataran Maybank) and Masjid Negara - at 10am.
"At 12.30pm the groups will converge on Dataran Merdeka and the rally program will commence before Officially ending at 6pm," a press statement by the group said.
"Personnel from the .NET Security Team, clad in purple, will be stationed throughout the three play areas: Bangsar LRT, Masjid Negara, and Dataran Merdeka. Comprising 1,400 personnel, they will handle all incidents of confrontation, violence, and general security," the release said.
If there is any provocation, the protesters should not get into any engagement but move away from the scene, they said.
The organizers have also given helpline numbers to help participants, especially those who face arrest. Those facing trouble on the rally day can contact the numbers 011-21376814 or 011-39376684.
For medical emergencies during the protest rally, people can call hotline at 011-39440069 where a 160-strong medical team will be on standby.
The social media handles of the movement -- Facebook, Twitter and Instagram -- will offer other details and information to the protesters.
