Samoa's ruling Human Rights Protection party has lost two MPs to the row over plans to change which side of the road vehicles drive on.
They are the former Minister of Broadcasting and Telecommunication in the last HRPP government, Palusalue Fa'apo II, and the Associate Minister for the Ministry of Justice and Courts administration, Muagututi' a Siaosi Meredith.
Both have now declared themselves independent MPs.
Their resignation reduces the number of seats held by the ruling HRPP from 35 to 33 in the 49 seat parliament.
They were the only government MPs who spoke against the controversial road traffic bill when the legislation was debated and passed for the second reading.
The HRPP is understood to have held a caucus meeting before the debate on the legislation where members were told to quit if they chose to speak against the bill.
The former Minister of Tourism and Trade, Hans Joachim Keil, was one of the MPs in the government who has shown opposition against switching the road side vehicles travel on when a parliamentary committee report on petitions against the change was debated.
But Mr Keil and other five opposing MPs including a cabinet minister have remained loyal to the party.