Speaking in Oslo, Norway, on Tuesday, Mu Sochua said the continued support for the election process offered a veneer of respectability to an otherwise corrupt process.
The Cambodia Democracy Act includes amendments that could see senior Cambodian officials linked to the crackdown face asset freezes and visa restrictions.
The parties called on the country’s election body, the National Election Committee, to take legal action against those calling for an election boycott.
The lawmakers were set to discuss the Cambodia Democracy Act and an amendment that could see Phnom Penh handed further sanctions over its crackdown on the opposition, civil society, and independent media.
Five political parties have so far successfully registered for the election, while a further 15 are having their applications reviewed.
Prime Minister Hun Sen has previously said that not voting in the election was tantamount to treason.
Members of opposition have called for boycott of July 29 vote but preparations are going ahead.
There are concerns for Kem Sokha’s health after he suffered a damaged shoulder, high blood pressure, and hyperglycemia.
The former opposition members are due to have their cases heard Thursday and could face between seven and 20 years in prison if their convictions are not overturned.
On April 30, the National Election Committee announced it was opening registration for parties who wished to contest the July 29 vote.
The May Day march on Tuesday was limited to a riverside space near the city’s landmark site of Wat Phnom and with a large security force presence.
Bun Chhay was arrested in August last year over a 2007 drugs case and another drugs bust in 2012 and charged with drug trafficking offenses.