VANCOUVER -- Christy Clark is warning the NDP that delaying work on the Site C hydroelectric dam in B.C. could cost taxpayers $600 million.

NDP Leader John Horgan wrote to BC Hydro last week asking it to suspend the evictions of two homeowners and urging it not to sign any new contracts on the $8.6-billion project until a new government has gained the confidence of the legislature.

But Clark says the evictions are necessary as part of a road and bridge construction project that are needed to divert a river in September 2019.

She says any delay could postpone the diversion by a year and cost of hundreds of millions of dollars.

The premier has asked Horgan to reply by Saturday on whether he still holds the same position.

Horgan has called for a review of Site C by the B.C. Utilities Commission but Clark says the project is likely to progress past the "point of no return" before a review can be completed.

The dam will be the third on the Peace River, flooding an 83-kilometre stretch of valley, and local First Nations, landowners and farmers have fiercely opposed the project.