PHNOM PENH (Reuters) - Cambodia’s election organizers said on Monday they will investigate a complaint against about 30 former opposition party members for calling for a boycott of Sunday’s general election.

A supporter of the ruling Cambodian People's Party (CPP) uses a mobile phone to photograph a portrait of CPP president Hun Sen during an election campaign in Phnom Penh, Cambodia, July 7, 2018. REUTERS/Samrang Pring/File Photo

The main opposition Cambodia National Rescue Party (CNRP) was dissolved last year, part of a wide-ranging crackdown by Prime Minister Hun Sen who is looking to secure his grip on power after a 2013 election which his ruling Cambodian People’s Party (CPP) narrowly won.

The Clean Finger boycott campaign, spearheaded by exiled members of the opposition, refers to the ink voters use to stain their fingers.

Authorities have said calls to boycott the vote are illegal, but rights groups argue the calls are not against the law.

Ven Porn, head of the election committee in Battambang province, said a CPP official had lodged a complaint against former CNRP members.

“We will investigate,” Ven Porn told Reuters on Monday.

With no significant competition left, Hun Sen, who has ruled Cambodia for 33 years, is widely expected to win on Sunday.

CNRP leader Kem Sokha was jailed in September on treason charges which his supporters say were politically motivated. He is currently in pre-trial detention near Cambodia’s border with Vietnam.

CPP spokesman Sok Eysan said the party sought to fine opposition members up to $5,000 for calling on people not to vote.

“This is incitement and a trick to prevent people from voting, which is against the citizen’s rights as stated in the constitution,” Sok Eysan said.

Chea Chiv, a former head of the CNRP in Battambang who was named in the complaint, said boycotting the vote was not illegal.

“I won’t vote if there is no party I like, and this is freedom of expression as guaranteed by the law,” Chea Chiv told Reuters.

Phil Robertson, deputy director of Human Rights Watch’s Asia division, expressed concern.

“... when people go to vote, they have to stick their finger into India ink and so they (authorities) will be able to determine very clearly who’s got an inky finger and who hasn’t,” Robertson told Reuters.

“The people who have not gone to vote may face some intimidation and harsh questions.”