North Carolina Sen. Thom Tillis says he'll vote to block President Donald Trump's emergency declaration at the border with Mexico, becoming the second Senate Republican to do so.

In an opinion column posted late Monday by The Washington Post, Tills says he agrees with Trump that there is a crisis at the border. But he says that as a senator, he has "grave concerns" about letting a president weaken Congress' power of the purse.

The declaration would give Trump access to billions of dollars more than Congress approved to build his proposed wall.

Tillis faces a potentially competitive re-election next year. So does Maine Sen. Susan Collins, the other Republican who has promised a no vote.

The Democratic-controlled House is set to approve the measure Tuesday.