The signs, which bear the slogan "Steady growth, good jobs," have popped up beside many construction sites. Brian Pallister said they usually contain no information about each road project and are essentially campaign signs for the NDP government.
"If the NDP wants to do pre-election advertising, that is well within their rights," Pallister said Thursday.
"But they should use their own money and not use the money they take from Manitobans."
Justice Minister Andrew Swan said the signs are similar to the federal government's "Economic Action Plan" billboards. He also said the signs let Manitobans know where their money is going.
"We know people will see that branding, will see that sign. They'll know where their tax dollar is being invested."
The infrastructure messaging has been a key point for the government since it raised the provincial sales tax last year to eight per cent from seven and saw its popularity plummet in opinion polls. It later promised to use all the money raised by the tax hike for core infrastructure work such as roads, bridges and flood-prevention projects.
In Ontario, the auditor-general's office reviews a wide range of government advertising for possible partisan messaging. The reviews cover government billboards for many construction projects but not highway work.