QUEBEC -- Quebec will introduce sliding-scale fees in its public daycare program, meaning higher payments based on family income, Premier Philippe Couillard announced Thursday.

While the current fee of $7.30 will remain in place, at least symbolically, families will pay more tax when they send in their annual return.

Families earning less than $50,000 as well as those on welfare will be spared any hikes.

Those with income of under $75,000 should end up paying $8 a day, while the fee is expected to climb to $11.75 for those earning $100,000.

A family earning $122,000 will pay $15, while those earning $150,000 will have to fork out $20.

Couillard said the daycare program will remain the most generous in the country and added that the government's decision is being driven by "social justice."

The financial contribution of parents will rise to 20 per cent of the overall cost of a daycare place from 13 per cent.

A daycare spot costs roughly $60 a day.

The fees will also be indexed, beginning in January 2016.

Couillard said the network costs the government $2.3 billion a year, a burden the government can no longer afford as it aims to clean up public finances.

Opposition parties, meanwhile, accused Couillard of betraying an election campaign promise to not hike taxes.

"Does the premier's word still have any worth?" asked Francois Legault, leader of the Coalition for Quebec's Future.

When the Parti Quebecois launched the widely acclaimed program in the late 1990s, parents paid $5 a day to send their children to daycare centres that receive government money.

In Ottawa, the federal New Democrats said the fact Quebec feels compelled to apply a sliding scale of fees underscores that party leader Tom Mulcair is on the right track in proposing a national universal, affordable daycare plan.

"Right now, they're doing it all on their own, without any help from the federal government," said NDP social development critic Jinny Simms.

"But if the federal government was doing their part, then they wouldn't feel the financial stretch or whatever they're feeling right now."

Under Mulcair's plan, to be phased in over eight years, an NDP government would spend $5 billion a year to create one million daycare spaces at no more than $15 per day.

The federal government would pick up 60 per cent of the tab, with the provinces paying the other 40 per cent.

The $15 cap is not hard and fast but Simms suggested there'd be no need to exceed that if Ottawa shouldered some of the cost.

Earlier this week, Ontario's governing Liberals endorsed Mulcair's proposal, supporting an NDP motion in the legislature.