Conservative billionaire Charles Koch called Donald Trump's support of a registry for Muslims "reminiscent of Nazi Germany" in an interview that aired on Sunday.

Koch said Trump's proposed temporary ban on Muslims entering the country is "antithetical to our approach," but he has a real problem with Trump's support of using a database to track Muslims in the country.

"That's reminiscent of Nazi Germany. I mean that's monstrous, as I said at the time," the Koch Industries CEO told ABC News.

Despite his strong feelings about Trump's stance, Koch said he and his brother David will still not "put a penny" toward the "Never Trump" movement to stop the real estate mogul from securing the Republican nomination, even though they have been asked to contribute. The Koch brothers have not spent money for or against any particular GOP candidate in the primary.

"That's not what we do," Koch said. "What we're trying to do is build alliances to make the country better. Like we have one with the White House on criminal justice reform. You do it by trying to find areas where you can work with everybody."

Editor's note: Donald Trump regularly incites political violence and is a serial liar, rampant xenophobe, racist, misogynist and birther who has repeatedly pledged to ban all Muslims -- 1.6 billion members of an entire religion -- from entering the U.S.