The Malaysian Communications and Multimedia Commission (MCMC) will block websites promoting, spreading information and encouraging people to join Bersih 4.
Citing a statement by the Home Ministry, the commission said the block was because these websites could threaten national stability.
"As such, MCMC would like to remind the public to be careful in sharing these websites on social media," said the commission in a statement today.
The Home Ministry has said that the Bersih 4 rally this weekend is illegal as it intends to incite the people against the government.
MCMC's announcement came just two days after newly-minted Multimedia and COmmunication Minister Salleh Said Keruak promised the government will not block the internet over Bersih 4.
MCMC, in its statement, cited three grounds by the Home Ministry in justifying its move to block pro-Bersih 4 websites.
The three grounds relating to Bersih 4 are as follows:
1. Operating illegally to spark unrest among the multi-racial and multi-religious population
2. Spreading seditious propaganda with negative intentions towards the government and distributing pamphlets that can be detrimental.
3. Its activities had tarnished the country's image and can threaten public order and safety, economic prosperity and national sovereignty as well as harmony in society.
The announcement comes despite the government's Multimedia Super Corridor Bill of Guarantees which promises no censorship of the internet.
Last month, MCMC also moved to block whistleblower portal Sarawak Report over its reports about alleged misappropriation by state-owned 1MDB and Prime Minister Najib Abdul Razak.
1MDB and Najib have denied the allegations.