New York (CNN) Friends of the Earth Action, an environmental advocacy organization, will start to air an ad supporting Vermont Sen. Bernie Sanders next week in Iowa and New Hampshire, CNN has learned.

The ad, which touts Sanders' positions on the Keystone XL pipeline and trade and does not mention Democratic frontrunner Hillary Clinton, will start airing on Tuesday in the Des Moines, Iowa and Manchester, New Hampshire media markets and will run for a week, according to Erich Pica, the group's president.

"Bernie Sanders had the courage to stand up against the Keystone pipeline from day one. He introduced the bill to keep fossil fuels in the ground on federal land and he opposes unjust trade agreements that damage our planet," says a narrator during the 30-second spot . "It is why Friends of the Earth Action urges you to support Bernie Sanders for president."

Sanders has emphasized his early opposition to the pipeline, in contrast to Clinton, who as secretary of state at one point said she was "inclined" to approve the project. Clinton last year eventually said she opposed the pipeline, and President Barack Obama killed the proposal in November.

Outside money influences

Friends of the Earth Action is a 501(c)(4) nonprofit organization, according to the Internal Revenue Service, that can engage in political activity as long as those efforts are not its primary purpose. In campaign finance parlance, the 501(c)(4) classification is sometimes referred to as a "dark money" group because there is no limit on the dollar amount supporters can give the the organization, and it is not required, according to the IRS, to disclose its donors.

The law bars Pica from contacting or coordinating with the Sanders campaign.

Sanders' has made campaign finance a key plank in his presidential campaign , pledging to overturn the 2010 Citizens United decision by only appointing justices to the Supreme Court who agree with him on that issue and pushing for a constitutional amendment "to regulate money in elections."

And the Vermont senator has made a point of disavowing super PACs, another form of outside group that is allowed to raise and spend unlimited amounts of cash, although those donors and actions must be reported to the FEC. Yet it has also allowed National Nurses United For Patient Protection, a super PAC, to continue spending hundreds of thousands of dollars working on the senator's behalf.

Friends of the Earth Action spokesman EA Dyson, said that its ad campaign was "paid out of individual donor contributions, the majority of which are under $200." Any donations over $200, Dyson said, would be disclosed on the group's website within 24 hours.

"No funds used in the creation or placement of the ads comes from any super PAC money," he said. "As you know, Friends of the Earth fights against the outsized influence of money in politics."

Michael Briggs, a Sanders spokesman, welcomed the ad in a statement early Friday evening and downplayed any concerns about the group.

"This is a grass-roots environmental organization and its political efforts are funded with small-dollar contributions from donors," Briggs said. "According to their statement, they intend to fully disclose their donors within 24 hours. Friends of the Earth Action is not a corporation looking to gut regulations or procure tax breaks -- they are an organization made up of thousands of American citizens concerned about a healthy environment and fighting climate change."

Pica said the group endorsed the senator last summer because it believes him "to be the best candidate to address the global challenges presented by climate change," adding that when Sanders' called to "create a political revolution," that meant "he needs everybody's help."

Pica said earlier Friday that the organization feels "this is the best thing we think we can do (for Sanders) right now."

"They don't know this is coming because we can't coordinate with them," Pica said.