The Khmer National United Party is to hold a congress on August 12 after several members were sacked from their roles as government officials.
KNUP member Harry Sam Ath confirmed the congress had been called because 17 party officials were ousted from their government positions last month, while several others defected to the ruling CPP.
The King in June also granted the Prime Minister’s request for KNUP president Nhek Bunchhay to be stripped of his role as a government adviser, which was equal in status to deputy prime minister.
Mr Hun Sen had asked for the KNUP leader to be punished following suspicion about his involvement with the opposition CNRP.
The CNRP has meanwhile begun distributing its new-look signs and banners across the country.
The government recently amended the Law on Political Parties to ban parties from using any imagery or voice recordings of convicts, effectively ending former CNRP leader Sam Rainsy’s political career.
The well known image of Mr Rainsy and CNRP leader Kem Sokha holding hands is being replaced by the slogan “United Rescue Our Nation” and the party’s sunrise logo.
CNRP spokesman Yim Sovann said the new signs will cost between $200,000 and $300,000.
Mr Sovann said the removal of Mr Rainsy’s image will not affect the party ahead of the general election in 2018.
“People already know who we are and what we stand for,” he said. “CNRP will win the election if it is free and fair.”
CNRP lawmaker Ou Chanrith said the cost of the new signs will be met by fundraising and donations from party supporters.
“We don’t have any challenges with the financial issue,” Mr Chanrith said.
The Sam Rainsy Party, which still has seats in the Senate, must change its name following the amendments.
Local media reported it will be known as the Candlelight Party.
SRP president Teav Vannol could not be reached for comment.