HALIFAX -- The union representing Nova Scotia's public school teachers took the next step in an increasingly fractious contract dispute Thursday, asking the provincial labour minister to appoint a mediator in an effort to stave off job action early next month.

The Nova Scotia Teachers Union announced via Twitter late in the day that president Liette Doucet had asked Labour Minister Kelly Regan to appoint a mediator to handle the dispute.

There was no immediate response from the government.

The union's request came shortly after Premier Stephen McNeil announced the launch of a government advertising campaign to explain its position in the simmering impasse.

McNeil said the campaign will include a series of Liberal party-funded and government-funded ads, saying that he had personally voiced a party ad the day before.

The party ads are television and Facebook videos that are scheduled to run sometime next week.

After weeks of a more conciliatory tone by the government, the move appears to mark a shift in the government's approach in a dispute where teachers can take strike action as early as Dec. 3.

"We'll continue to articulate to Nova Scotians in every means possible why we believe this (contract offer) is fair and on investments we've made in the classroom," McNeil said.

There were no details on how much the campaign would cost, but McNeil defended the impending campaign, saying the government has a responsibility to communicate with the public.

Opposition Progressive Conservative Leader Jamie Baillie said the ad campaign shows the premier is more interested in "saving his own political skin" than solving the contract impasse.

"If he has money for (government) ads then he has money to improve the classroom," said Baillie.

NDP Leader Gary Burrill said McNeil had adopted a more negative tone in recent days when talking about teachers' benefits and pay packages, and if he has a message to deliver, it should be done at the negotiating table.

Attempts to move the dispute to conciliation were scuttled Tuesday when the sides couldn't agree on the terms for returning to talks.

The appointment of a conciliation board would have delayed job action while the board was at work, pushing back a potential strike.

Union members voted 96 per cent in favour of strike action last week after voting earlier last month to reject the province's latest contract offer -- the second time this year they turned down a tentative agreement.

The rejected deal contained a two-year wage freeze, followed by a one per cent increase in the third year, a 1.5 per cent increase in the fourth year and a 0.5 per cent increase at the end of the fourth year.