With Democratic rival Bernie Sanders surging in the polls, Hillary Clinton came out to strongly denounce the Vermont senator's record on gun control Tuesday.

In an interview with MSNBC, Clinton called attention to Sanders' past support for a bill that she called the National Rifle Association's "most important priority in 20 years."

"When it really mattered, Sen. Sanders voted with the gun lobby, and I voted against the gun lobby," Clinton said.

Sanders voted in support of the 2005 bill that would grant immunity to gun makers from lawsuits when their weapons were used in crimes. When pressed on the issue, Clinton added, Sanders refused to give a straight answer.

"You know, maybe it's time for Sen. Sanders to stand up and say 'I got this one wrong.' But he hasn't," Clinton said. "He's defended his vote time and again."

This latest criticism from Clinton comes shortly after President Obama's push to increase gun safety regulations.

Last Thursday, the president published an op-ed in The New York Times, in which he said he would "not campaign for, vote for or support any candidate" who did not support commonsense gun reform, regardless of whether the candidate were a Democrat or not.

Sanders responded to the piece in an interview with MSNBC Friday, saying he didn't believe the statement was aimed at him, given his support of gun reform.

"You know, there are a lot of candidates and money in the House and the Senate who may be opposed to sensible gun control legislation," Sanders said. "I happen not to be one of them. I strongly support the executive order that the president is working on right now."

Recent polls have shown that Sanders is gaining major ground in vital states such as New Hampshire and Iowa, posing a major threat to Clinton's position as the Democratic front-runner.

Clinton made an appearance at an event at Iowa State University on Jan. 5, in which she called out Sanders, whose campaign has centered on standing against Wall Street and big money corporations.

"If you're going to go around saying you'll stand up to special interests, well, stand up to the most powerful special interest -- stand up to that gun lobby," she said, according to The New York Times.