Swelling U.S. power prices may rise even faster in some parts of the country if 10% energy tariffs imposed by the Trump administration this week hit Canadian electricity supplies and trigger retaliation,

Ontario’s leader said he will add a 25% export tax on electricity sent to New York and other states in retaliation for Trump’s tariffs. Ontario provides 2,500 of the 4,600 megawatts of capacity that New York draws upon from Canada, the NYISO reports.

U.S. electric-grid operators still don’t know whether President Trump’s looming tariffs will apply to imported supplies that help power homes across New England and New York. The nonprofits that oversee grids in those regions believe the answer is no,