The Trump administration is stepping up pressure on trading partners to quickly make new deals before a Wednesday deadline, with plans for the United States to start sending letters Monday warning countries that higher tariffs could kick in Aug.

The president said he would cease negotiations and impose new tariffs because of Canada’s imminent, new digital services taxes.

WASHINGTON—President Trump said he terminated trade talks with Canada over what he called an “egregious” digital-services tax on U.S. tech companies, plunging relations with America’s second-largest trading partner back into turmoil.