Starting today, Ontario is hitting the United States with a 25% tax on exported electricity, a move that will hike energy costs for 1.5 million homes and businesses across New York, Michigan, and Minnesota. Premier Doug Ford and Energy Minister Stephen Lecce are set to address the measure at a Queen’s Park news conference this morning, where they’ll outline how the province plans to enforce the levy.

The tax marks Ontario’s latest salvo in a tit-for-tat trade spat with the U.S. Other retaliatory steps include yanking American liquor from LCBO shelves and locking U.S. firms out of roughly $30 billion in provincial contracts. Ford has warned he could crank the electricity tax up to 50% if President Donald Trump keeps up what he calls an “economic assault” on Canada, though he’s stayed vague on what would trigger such a hike.

“Trump’s tariff threats won’t go unanswered—we’ll keep pushing back until they’re gone for good,” Ford posted online last week.

The trade clash heated up when Trump rolled out a 25% tariff on most Canadian exports last week, only to pause the levies on goods covered by a North American trade deal until April 2. Ontario, however, isn’t backing down.

The move has sparked concern south of the border. The New York Independent System Operator, which manages New York’s power grid, has cautioned that the tightly linked U.S.-Canada electrical network—one of the world’s most interconnected—could face reliability risks and market disruptions due to the tax.