As the presidential primary contenders campaign in New York, Sen. Bernie Sanders (I-Vt.) is hoping his position on hydraulic fracturing can help differentiate him from former Secretary of State Hillary Clinton.

In an ad and speech Monday, Sanders calls for an outright ban on hydraulic fracturing, or fracking, a process used to extract natural gas reserves from shale formations. Fracking uses a high-pressure stream of water, sand and chemicals to tap into shale formations. And there is a lot of natural gas contained in the Marcellus formation, which stretches up into New York state.

But the issue has been hotly contested in New York. Gov. Andrew Cuomo announced a ban on the process in December 2014 due to concerns about health and safety. The ban was finalized in June 2015.

Many communities have raised concerns that fracking could contaminate groundwater sources, which is what prompted the New York state ban. The Environmental Protection Agency released a long-awaited study on the impact of fracking on drinking water sources last year, which found that while there have been some cases of contamination, it is not a widespread issue. The EPA's own science advisory board has criticized the study, however, saying its conclusion "requires clarification."

Sanders called for the New York ban to go national at an event in Binghamton, New York, Monday. “I want to applaud you for standing up to Gov. Cuomo and demanding that New York state ban fracking," Sanders said. "If we are serious, we need to put an end to fracking not only in New York and Vermont but all over this country."

His ad, also released Monday, set this up as a key difference between him and Clinton.

"Bernie Sanders is the only candidate for president who opposes fracking everywhere," says the 30-second advertisement, narrated by actress Susan Sarandon. The ad cites concerns over "dangerous, cancer-causing chemicals" being injected into the ground. And it intones that Washington politicians are siding with polluters over families, because they've been influenced by Big Oil money.

"He can't be bought by them, because he's funded by you," says the ad.

The Sanders campaign clearly sees fracking as an issue it can use to distance his policy proposals from Clinton. While Sanders has said he would ban the practice, Clinton has staked out more of a reformist position. She has said she would impose tougher regulations and more restrictions on fracking, and that states and local governments who want to ban fracking should be able to, but still believes that there are ways to "ensure safe and responsible natural gas production."

"By the time we get through all of my conditions, I do not think there will be many places in America where fracking will continue to take place," Clinton said in a debate last month.

In the past, Clinton has been more supportive of natural gas as a "bridge" fuel as the country moves to renewable energy -- which is pretty much the position the Obama administration has taken on gas.

Sanders and Clinton have been sparring over oil and gas in recent weeks. A climate activist confronted her over campaign donations from the fossil fuel industry, which prompted the former secretary of state to say that she is "so sick of the Sanders campaign lying about me."

Sanders has said that Clinton "gets a lot of money" from the fossil fuel industry, among other industries. And his campaign put out a statement saying that Clinton "has relied heavily on funds from lobbyists working for the oil, gas and coal industry."

Clinton's campaign has countered that she has "not taken a dollar from oil and gas industry PACs or corporations." She does, however, take individual contributions from people who work in the industry. The Huffington Post covered those contributions last year, noting that many of her major bundlers also lobby for the fossil fuel industry.

But the fact-checkers have sided largely with Clinton, noting that even if she takes more money from individuals who work in the fossil fuel industry than Sanders, it's hardly a substantial portion of her campaign funds.

The new Sanders ad indicates that his campaign sees oil and gas -- and fracking specifically -- as a key issue for next week's New York contest.