U.S. President Barack Obama is threatening to use his veto power if Republicans try to repeal Obamacare or loosen environmental regulations in the new Congress. Reuters

U.S. President Barack Obama’s veto pen will get more active in the new Congress if the body tries to roll back Obamacare or loosen environmental regulations, the president warned in an NPR interview scheduled to air Monday, the Associated Press reported. Republicans will hold majorities in both houses for the first time in Obama’s presidency when the next Congress convenes on Saturday.

Obama has vetoed only two bills since he took office in 2009, according to Senate records. That’s the fewest number of vetoes since President Warren G. Harding used six from 1921-1923. "I haven't used the veto pen very often since I've been in office. Now, I suspect, there are going to be some times where I've got to pull that pen out,” Obama said in the interview, conducted by NPR before the president left for Christmas vacation in Hawaii. "I'm going to defend gains that we've made in health care. I'm going to defend gains that we've made on environment and clean air and clean water."

Even though the GOP will control both houses of Congress in January, they would need a two-thirds vote in the House and Senate to overturn an Obama veto. If members voted along party lines, Republicans couldn’t overcome a veto since they will have 54 percent of the seats in the Senate and about 57 percent in the House.

Incoming Senate Majority Leader Mitch McConnell, R-Ky., indicated that he would work with Democrats on jobs bills. "Bipartisan jobs bills will see the light of day and will make it to the president's desk, and he'll have to make decisions about ideology versus creating jobs for the middle class," he told the AP. "There's a lot we can get done together if the president puts his famous pen to use signing bills rather than vetoing legislation his liberal allies don't like."

Changes to Obamacare, ranging from tweaks to a full repeal of the health care law, are also among Republican priorities. But the GOP would need Democrats to vote with them to withstand an Obama veto. U.S. Sen. Ted Cruz, R-Texas, suggested earlier this year that it is in Democrats' interest to side with Republicans on Obamacare if they want to keep their jobs.

“If there’s one thing that unifies politicians of both parties, you know, their top priority is preserving their own hide,” Cruz told ABC. “And if enough congressional Democrats realize they either stand with Obamacare and lose, or they listen to the American people and have a chance at staying in office, that’s the one scenario we could do it in 2015. If not, we’ll do it in 2017.”