Vanuatu's Opposition Leader claims a number of foreign nationals have been granted citizenship without meeting the necessary requirements.
Ralph Regenvanu said the Constitution was clear on people gaining citizenship by naturalisation.
He said people were supposed to live in Vanuatu for 10 continuous years before they could be granted citizenship by naturalisation.
"We are aware that number of individuals who have not satisfied the requirement of 10 years continuous residence in Vanuatu have now obtained citizenship by naturalisation.
"We are aware that the processes in the citizenship commission have not been properly followed, the law has not been followed and there is in breach of Constitution with regard to the giving of these citizenships and it's something we want investigated."
Reganvanu said if the government didn't deal with the issue, the Opposition would. He did not elaborate further.
Earlier this month the Chair of Vanuatu's Citizenship Commission claimed revenue collected over the past three months as part of its citizenship programme had skyrocketed to about $US84 million.
However Ronald Warsal said the government had tightened security and due diligence measures to ensure that all applicants had clean criminal records.
The chair said while the government was generating much needed revenue, it was also aware of concerns from the public concerning the programme.
In 2017, Vanuatu's passport law was amended to enable the citizenship sale program.