Hillary Clinton received the endorsement of the deep-pocketed League of Conservation Voters Action Fund Monday in New Hampshire, the environmental group confirmed to MSNBC.

Clinton was joined by the group’s president, Gene Karpinski, and former Environmental Protection Agency head Carol Browner at an “Environmentalists for Hillary” event in Nashua where she’ll officially pick up the nod.

RELATED: Democrats go big on climate change, small on details

It’s the earliest LCV has endorsed a presidential candidate. The group is consistently one of the biggest spenders on the Democratic side of the aisle, dropping nearly $30 million in the 2014 cycle alone. Clinton keynoted the group’s annual fundraising dinner in December of last year and made a hard pitch for why she’s a committed green, receiving praise from Karpinski.

The LCV scores members of Congress and Senate on their environmental record, and actually gave a higher rating to Clinton’s chief rival for the nomination, Vermont Sen. Bernie Sanders. Clinton has a lifetime rating of 82% compared to Sanders 95%.

Close video Hillary Clinton moves left on key issues Hillary Clinton is gearing up for the first Democratic debate and she’s very busy protecting her left flank against Bernie Sanders. She’s moving left on trade, guns, Keystone, even Wall Street… but not everyone’s convinced. The Hardball Roundtable… Hillary Clinton is gearing up for the first Democratic debate and she’s very busy protecting her left flank against Bernie Sanders. She’s moving left on trade, guns, Keystone, even Wall Street… but not everyone’s convinced. The Hardball Roundtable… share tweet email Embed

But Karpinski told The Washington Post the group decided to endorse Clinton because they are so concerned about a Republican winning the White House and rolling back the Obama administration’s environmental legacy, much of which was accomplished through executive action. The group also noted that Clinton’s score may be artificially low because it counts missed votes as “nos” and Clinton missed several votes in the Senate while running for president in 2008.

Sanders has so far been endorsed by Friends of the Earth Action, which is considered a somewhat more radical environmental group.

All three Democratic candidates – Clinton, Sanders, and former Maryland Gov. Martin O’Malley – have vowed to make fighting climate change a top priority if they win the White House.