Sam Rainsy, who is on a US tour to build political support, said he was not confronting Prime Minister Hun Sen, but rather Vietnam.
Global Witness also revealed a series of what it called "high level corruption and governance failure" over the last 18 months.
Critics of the anti-corruption law have said it lacks the teeth to root out the country’s endemic corruption.
Mu Sochua said she would not pay the fine.
Cambodia insists it has been transparent in managing state revenue.
The ministry received 5,000 complaints since the beginning of 2009 from all around the country and has resolved 70 percent of them.
A donor meeting Wednesday and Thursday will focus on the government’s national development plan.
A judge says an investigation into further cases cannot take place until the court deals with its second trial.
Shareholders last week voted in favor of more transparency in payments to host countries like Cambodia.
Two men were accused of incitement in an ongoing land dispute between villagers and a powerful ruling party senator.
The order now gives officials more authority to act against squatter communities who may not be getting enough compensation.
It is not uncommon for companies to pay bonuses for concessions here, but what happened to that money remains unknown.