Kong Sam Onn, was the representing lawyer for opposition politician, Ms. MU Sochua,   in a case against Prime minister  Hun Sen who allegedly defamed her.

Kong Sam Onn attended a press conference to seek an apology and announce the forthcoming law suit by his client.

After Kong Sam Onn commenced the lawsuit he was charged with defamation under UNTAC Penal

Code Article 63 along with Mu Sochua.

The lawyer for Mr. Hun Sen, Mr. Ky Tech,   file a complaint against Kong Sam Onn to the Bar Council alleging that Kong Sam Onn violated Bar Association rules by asserting during a press conference held April 23 - three days before Mu Sochua's suit was filed - that Hun Sen defamed her.

On 18 June, the Bar Council made a decision that Kong Sam Onn had breached articles 4, 6 and 15 of the Bar Code of Ethics and  disbarred him from practising laws.

Bar Secretary General Suon Visal acknowledged  that two council members - whom he declined to name - held positions in the government, but said this would not affect the final decision.

After saying  he believed the council was not independent, adding that he would appeal the decision, Kong Sam Onn , reportedly under extreme pressure , wrote an apology letter to Prime Minister Mr. Hun Sen, withdrawing from representation of Mu Sochua and Ho Vann on July 7, 2009.

 When he apologised to Mr. Hun Sen and joined his party, all charges against him were immediately dropped and cleared, paving the way for him to practise laws again.

Kong Sam Onn also represents another opposition parliamentarian, Mr. Ho Vann who is charged with defamation and incitement. Mu Sochua’s and Ho Vann’s parliamentary immunity was lifted in a closed meeting of the National Assembly on 22 June 2009.

Since Mu Sochua and Ho Vann are reportedly having difficulty finding another lawyer to represent them.