"This is why ... we feel obliged to suspend, effective now and until further notice, our participation in the work of this [National] Assembly, until proper security conditions are established."
An MLC spokesman said that the statement had been read to a joint session of parliament late on Friday.
MP's home 'ransacked'
Luhaka said the party's decision not to participate in parliament was taken after the home of one of the party's MPs was ransacked by about a dozen Republican Guards.
He added that there was a "targeted and programmed operation" against MLC members.
Jean-Pierre Bemba, the party leader and defeated presidential candidate, left for medical treatment in Portugal on Wednesday.
Bemba had been living in the South African embassy in Kinshasa, Congo's capital, since March when government troops clashed with his bodyguards when they refused an order to disarm.
On Tuesday, the public prosecutor requested permission from the head of the country's new senate to prosecute Bemba as the "intellectual author" of the violence in the capital, which is believed to have left up to 600 people dead.
The charges against him include threatening internal state security, murder, armed robbery and destruction of property.
An MLC spokesman said the party's suspension of National Assembly activities did not affect senators, who are expected to vote on whether to lift Bemba's immunity once the Supreme Court approves bylaws for the Senate, which could take another week.