Bersih has urged the Election Commission (EC) and police to act against Umno acting chairperson Mohamad Hasan for exposing his ballot paper.
The electoral watchdog was referring to the candidate for the Rantau by-election flashing his ballot paper after marking it and before placing it in the ballot box.
“Does he not know that it is an election offence to breach the secrecy of a vote, even one's own vote, or did he do it in defiance of the law?” said the Bersih steering committee in a statement.
Bersih pointed out that Section 5 of the Election Offences Act 1954 underlined the importance of maintaining the secrecy of voting and information related to voting.
The penalty for breaching secrecy is up to one-year imprisonment or RM3,000 or both.
Bersih said when a person, especially an influential individual, exposes his or her ballot paper, it could influence how others vote.
“It could even facilitate the buying and selling of votes. Such a breach by Mohamad, if not dealt with, might encourage others to flagrantly expose their votes in future elections.
“This could have serious consequences related to the offence of campaigning on polling day and corruption,” it added.
Describing Mohamad's action as a defiant act to break election laws, Bersih said a strong message must be sent that secrecy must be maintained during voting and that no one is above the law.
Earlier, Malaysiakini called the Rantau by-election in Mohamad's favour after the votes he garnered surpassed the minimum threshold to score a win.
The Umno leader faced three contestants, PKR's Dr S Streram and two independents.
In the last general election, the former menteri besar won the seat uncontested after Streram was barred from filing his nomination papers.
Streram filed an election petition and the courts ordered that a by-election be held.