Labour MP Stuart Nash has renewed his call for an inquiry into petrol prices.
He says importer margins have risen to levels that previously prompted concern.
In February, Energy Minister Simon Bridges confirmed he had written to the big five petrol retailers.
He told BP, Mobil, Chevron, Gulf and Z Energy he was "disappointed" that as crude oil prices fell in late 2014, their margins had risen.
He said if they didn't pass on lower costs to consumers more promptly in future, he would "assess his options".
Prices started falling about the time he wrote to the companies, and Mr Bridges later said they were at acceptable levels.
At the time, Mr Nash asked Parliament's finance and expenditure committee to hold an inquiry, but a majority of its members voted against his proposal.
He said on Friday importer margins jumped to around 40c per litre in December and January, which prompted Mr Bridges to write to the companies.
"The margin is now 38.5c per litre, the level where the chairman of the committee has said he would consider an inquiry," Mr Nash said.
"The time for that inquiry has come."