The group of Vietnamese Christians has repatriated voluntarily despite alleged persecution in their homeland.
A ruling party lawmaker says he was stripped of parliamentary immunity by a 2013 conviction.
The Southeast Asian nation will hold its own general elections in July 2018.
They say worsening relations could threaten upcoming elections.
They have rounded up suspects in an incident where apparent illegal loggers killed two officials on forest patrol and wounded another.
The order comes as opposition MPs announce a boycott of parliament citing safety concerns.
A government official says the Dak Dam zone in Mondulkiri province is part of Cambodia.
But suspicions remain that others had organized the assault and the lawmakers party wants more suspects detained.
The party also wants the UN to investigate the beating of two of its lawmakers.
Drivers describe taking nearly 200 young men by truck from the PM's bodyguard base to the National Assembly.
But some say he is trying to fix a situation he allowed to get out of hand.
Accused of killing villagers by black magic, he was bludgeoned and stoned by a mob of hundreds.
The move comes following an investigation of Vietnam Rubber Group’s plantation activities in Cambodia.
The assaults occur during a pro-ruling party demonstration outside the parliament building.
They say the guards shot at them when they asked to cut trees on a local land concession.
Observers suggest the move is meant to consolidate the leader’s grip on power.
They say soldiers are using rifles to chase them off their farmland.