Faumuina Wayne Fong had been critical of Tuilaepa Sailele Malielegaoi's constitutional amendments that affect the judiciary and customary land.
Tuilaepa confirmed that Faumuina was made to quit at a caucus meeting last Friday.
The prime minister told reporters the Faleata urban seat MP was sacked because of his views against government policies.
Tuila'epa said the Human Rights Protection Party (HRPP) did not need that kind of MP.
