Hillary Clinton has hired a former lobbyist for the company behind the Keystone XL pipeline, further upsetting environmentalists who have long been wary of her commitment to fighting climate change.

BuzzFeed’s Ben Smith reported on Wednesday that the Clinton campaign has hired Jeffrey Berman as a campaign consultant. Berman, who began working for the campaign earlier this month, once lobbied on behalf of TransCanada, the company that hopes to build a pipeline carrying tar sands oil from Canada to the southern coast of the U.S.

R.L. Miller of Climate Hawks Vote said Berman's hiring "is a disappointment—especially as Martin O'Malley is taking flight based on the best climate plan I've seen from a candidate, and Bernie Sanders continues to soar."

"For us it’s a signal that she continues to be willing to work with oil and gas interests and take money from folks who are committed to have a pathway to fossil fuels," said Ben Schreiber, Friends of the Earth's climate and energy program director.

In 2008, political operatives described Berman as an “unsung hero” of Obama’s upset win over Clinton, due to a strategy that won Obama more delegates in key primaries when Clinton was still ahead in the popular vote. After Obama’s win, Berman joined the lobbying firm Bryan Cave LLC, which retained TransCanada as a client until 2013.