National Party leader John Key has warned his transport spokesperson to take care with his comments.
The opposition party was forced into damage control mode on Monday after Maurice Williamson said some motorists could pay up to $50 a week for the cost of new roads.
Mr Williamson was forced to "clarify" his comments, made on Sunday, after the party moved to assure the public that it has made no decision about road tolls.
He refused to speak to the media about the comments on his way into National's weekly caucus meeting on Tuesday.
But Mr Key had a message for him: "If National wants to win the election it needs to be disciplined and it needs to be on message - and I've made that position clear to Mr Williamson."
Deputy Prime Minister Michael Cullen says clarifying MPs' comments is becoming a trend for National after its labour and finance spokespeople were forced to make similar retractions.
Dr Cullen questions how National can run the country if it cannot run an opposition party.
"There's things that unite and divide our two caucuses. We both start with apologies at caucus - ours are (for) people who are absent, and theirs for what they said in the last week."
Parliament resumes on Tuesday afternoon after a two-week recess. The Government is likely to use Mr Williamson's comments to repeat its claim that National has a secret agenda.
National deputy leader and finance spokesman Bill English earlier described Mr Williamson's comments as "a bit exuberant".
Mr English says New Zealand has little opportunity for tolls because it does not have the traffic volumes of countries such as Australia. No decisions have been made, and $2 tolls, rather than $3-$5 charges, are more reasonable.
Transport Minister Annette King says the Government has built considerable infrastructure without the need for partnerships with the private sector. She said such partnerships are not a panacea for roading because projects have to be a certain size to attract private funding.
The law says no one can be forced to pay a road toll when no alternative route is available.
