Rep. Ryan Zinke (R-MT), a freshman congressman and retired Navy SEAL commander, is calling out his fellow Montanan, Democratic U.S. Sen. Jon Tester for Tester’s role in helping Senate Democrats obstruct efforts to have a vote on the House-passed Department of Homeland Security (DHS) funding bill.

Tester and all Senate Democrats have been blocking votes not just for cloture on the bill, but even on the motion to proceed—a rare and unusually bold tactic of obstruction—because they don’t like the fact that the House-passed bill blocks funding for President Barack Obama’s executive amnesty actions.

“There are some things that are not negotiable,” Zinke said when asked for his thoughts on Tester’s obstructionism in an interview in his U.S. House office on Capitol Hill on Thursday morning.

As a former Commander, I gave an oath to defend the Constitution against all enemies foreign and domestic. As a state senator, I gave that same oath. As a Congressman, I gave an oath to defend the Constitution. There are some things that are not negotiable: Faith, my family, and the Constitution are dead center. It is non negotiable to me. Whether the president likes a law or dislikes a law, he does not have the authority to write a law. On this issue, it is not negotiable.

Tester has said that he’s opposed to executive amnesty, but that’s not how he’s voting in the Senate.

“I would prefer the Congress acted, yes,” Tester said in November, according to Reuters, when asked if he thinks Obama should issue his then-forthcoming executive amnesty.

Zinke specifically called on Tester to back the House-passed DHS funding bill, and stop helping Senate Minority Leader Harry Reid obstruct votes on the bill.

“I would encourage my friend, my fellow legislator, Sen. Tester, to uphold his duty and to reject the president’s unlawful and unconstitutional actions,” Zinke said.

It isn’t just about immigration. It’s about the unconstitutional overreach of the president, to disregard Article I or Article II of our Constitution. The bill, I think it’s an appropriate bill. I would encourage Sen. Tester to pass the bill and uphold his duty. If the president wants to talk about immigration, then let’s talk about immigration. That means we’ll sit down with the president and go through reasonable immigration reform and probably negotiate out some of the amendments that were there, but you have to work it in the terms of the Constitution. I’m not going to blink.

Zinke added that Tester is “in a tough spot” because as chairman of the Democratic Senatorial Campaign Committee (DSCC), “he’s raising money for Elizabeth Warren” and for “many in the Democratic Caucus who don’t represent Montana values.”

“So I’m hopeful that Sen. Tester ends up sticking up for Montana and that does his duty to Montana values,” Zinke said. “And I would guarantee you, Montanans respect the Constitution of the United States.”

Zinke added that he would say the exact same thing to Tester if he saw him face to face.

“I maintain a cordial relationship with Sen. Tester,” Zinke said. “I have coffee with him every Wednesday. But, there are some things are not negotiable. At the end of the day, I think you’re on high moral ground when you respect Montana and you respect the Constitution and you do your duty as a Senator. We need to put Americans’ and Montanans’ interests in the front seat, and politics in the back.”

Zinke has succeeded before in getting Tester to back off his support for Obama’s and Reid’s liberal policies. Despite publicly stating he backed the Keystone XL Pipeline, Tester voted against it in the Senate a few weeks ago. Zinke called him out for it, and then Tester—under immense pressure back home in Montana after a Breitbart News story went viral in state—flip-flopped back and started supporting the Keystone pipeline yet again, voting in favor of it.

It remains to be seen if Tester will keep supporting Obama and Reid here, or if he’ll join Zinke in supporting “Montana values.” Tester’s communications director has not responded to a Breitbart News request for comment.