Two GOP senators -- John McCain and Ben Sasse -- announced Wednesday that they oppose President Trump's nominee for U.S. Trade Representative, Robert Lighthizer, because of his position on NAFTA.

"Unfortunately, your confirmation process has failed to reassure us that you understand the North American Free Trade Agreement's (NAFTA) positive economic benefits to our respective States and the nation as a whole," the two senators wrote in a letter to Lighthizer.

McCain and Sasse said Lighthizer's skepticism of NAFTA is well-known, which they said they find "alarming."

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"America deserves a USTR who will renegotiate NAFTA in order to build on its successes, not as a pretext for unraveling it. Mexico and Canada are two of our largest export markets and the free movement of goods is essential to the growth of our national economy," they wrote.

Despite their opposition, Lighthizer is expected to receive bipartisan support, but even if Democrats decide to band together and vote against his nomination, Republicans could still confirm him with the help of Vice President Mike Pence, who could break a tie.

Lighthizer was previously a deputy U.S. trade representative under President Reagan and has since worked as a trade attorney in Washington, D.C.

CBS News' Alan He contributed to this report.