The Solomon Islands opposition leader says the chairman of the government caucus, the MP Namson Tran, was granted citizenship illegally.
Derek Sikua has filed for a judicial review into the granting of Solomon Islands citizenship to the Vietnamese-born West Honiara MP.
Dr Sikua has told the Solomon Star he obtained copies of documents concerning what he described as the approval of Mr Tran's citizenship application in 2001.
He says this was done in total disregard of the 10 years residence requirement.
Dr Sikua says he is concerned that an unqualified MP is in parliament.
The prime minister's office has dismissed the claim, saying Mr Tran has in his possession a valid citizenship certificate.