The source said the proposed deal was expected to cut top-line tariff rates on Canadian-built cars and trucks to 15% from the existing 25%. ​Industry executives say that rate threatens to kill domestic auto manufacturing, reports David Shepardson and Promit Mukherjee at Reuters.

Two auto executives said Canada was pushing to reduce the tariff to 10%.

The 15% top-line autos tariff also would come before deductions for the value of U.S.-produced content, bringing the effective rate substantially lower, the source told Reuters. The proposed deal would also halve the top-line tariff rates ​on Canadian steel and aluminum to 25%, the source said.