A Republican proposal aimed at cutting tax rates and keeping jobs in the U.S. risks whacking the earnings of big U.S. retailers by driving up the cost of imported clothes, furniture and other goods.

Among the companies whose earnings are calculated to take a hit under the so-called border-adjusted tax proposal are Wal-Mart Stores Inc., Costco Wholesale Corp., Genuine Parts Co. and Dick’s Sporting Goods Inc., analysts said.

The...