OTTAWA -- New mothers and fathers planning to begin their parental leave on or after Dec. 3 will be able to spread their federal benefits over a longer period of time.

The federal government's long-promised changes to parental leave rules will go into effect early next month, says Families Minister Jean-Yves Duclos, allowing eligible new parents to take up to 18 months of employment insurance benefits after the birth of a child.

On that same date, a new family caregiver benefits will also kick in -- one a 15-week leave to care for a critically ill or injured adult, the other a 35-week benefit to care for a critically ill or injured child.

Eligible soon-to-be-mothers will also be able to claim maternity benefits up to 12 weeks before the baby is due.

However, the government won't increase the actual value of employment insurance benefits for anyone who takes the extended parental leave: instead, the Liberals are sticking with their 2015 election promise to spread 12 months' worth of benefits over 18 months.

The change in rules will automatically give more workers in federally regulated workplaces like banks, transport companies, the public service and telecoms the option of taking time off, and are likely to spur calls for provincial changes to allow the other 92 per cent of Canadian workers access to similar leave.

So far, Ontario has publicly said it will amend its legislation to match the new federal rules.

Affected workplaces will have to decide how -- or even if -- to amend existing leave policies and collective agreements that spell out issues like salary top-ups.

As is, the federal parental leave program pays out benefits for up to 17 weeks for new mothers and allows parents to split an additional 35 weeks.

Under the changes first outlined in this year's budget, new parents apply for employment insurance benefits, they will be able to decide whether to take additional weeks off, which can be split between parents.

Anyone who is already receiving 35 weeks of parental leave before the new measures officially come into effect won't be able to switch and take the extra time.

The eligibility for the cash won't change: A new parent will still need 600 hours of work in the previous 12 months to access benefits, while self-employed workers who have opted in to the EI system will need to have earned at least $6,888 in the last year.

The Liberals budgeted $886 million over the next five years for the new measures, and $204.8 million a year after that.

None of the parental leave changes will impact residents of Quebec, where the province runs its own parental leave program.