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.
American Daniel Stephen Johnston has already spent a year in prison in Cambodia and will likely serve more jail time after he is sentenced in August.
The Cambodian courts are due to announce a verdict for the two jailed journalists on Friday.
Prime Minister Hun Sen has previously said that not voting in the election was tantamount to treason.
The Phnom Penh Post’s sale to a Malaysian PR firm linked to the ruling CPP sparks concerns over a loss of independence among its readership.
The World Bank said growth in Cambodia had slowed about 6.8 percent in 2017, slightly down from 7 percent in 2016.
American president Donald Trump will meet Korean leader Kim Jong Un on June 12 in Singapore.
Members of opposition have called for boycott of July 29 vote but preparations are going ahead.
Les Kosem was involved in the now-defunct United Front for the Liberation of Oppressed Races, better known by its acronym, FULRO.
The Apsara Authority said that the men were construction workers employed by a Chinese company and they did not inform the authorities before they started drilling at the site.