Rep. Justin Amash slammed President Trump's "unlawful" executive order barring certain immigrants from entering the U.S.

Demonstrating once again that he is among the most principled members of Congress, the libertarian-leaning Republican from Michigan neatly laid out the case against Trump's latest pronouncement.

"It's not lawful to ban immigrants on basis of nationality," Amash wrote on Twitter. "If the president wants to change immigration law, he must work with Congress."

On his Facebook page, Amash explained that immigration law prohibits the government from denying entry to legal immigrants because of their country of origin, as Trump has done. And while it is legal for the government to prohibit refugees from entering, "banning all refugees from particular countries is harsh and unwise," wrote Amash. "We still should admit well-vetted persons."

President Obama's executive order did not violate the law, according to Amash, because it only applied to refugees.

Unfortunately, there are very few people in Congress who are willing to call out their own party when its leader breaks the law and undermines the rights of American citizens.

Admitting that both parties routinely ignore the Constitution, reject the Rule of Law, and erode liberty is the first step to recovery. — Justin Amash (@justinamash) January 30, 2017

In the Senate, Republican Sen. Ben Sasse has also criticized Trump's immigration order for being "too broad." Sens. John McCain and Lindsey Graham have expressed concern as well.

For more on the Trump administration's misguided anti-immigration crusade, read Reason's Nick Gillespie.