Green group targets Sen. Scott Brown with $1.8 million ad buy

The League of Conservation Voters also takes aim at the senator for receiving campaign contributions from the oil industry and for voting to delay Environmental Protection Agency climate change regulations. Brown received a zero percent score on the group’s 2010 National Environmental Scorecard.

“Scott Brown’s gone to Washington. And something’s gone horribly wrong,” the ad says. “Brown sided with big oil — taking thousands from oil companies just weeks before he voted to keep their special tax breaks.”

The league’s spokeswoman says the advertisement is about “public education and legislative accountability,” not the Massachusetts Senate race.

The advertisement comes as Brown is facing off against Democrat Elizabeth Warren in a close race to keep his seat.

A UMass-Lowell/Boston Herald poll released in early October showed that Brown is in a dead heat with Warren, a Harvard professor who was tapped by President Obama to set up the Consumer Financial Protection Bureau.

Jim Barnett, Brown’s campaign manager, called on Warren to denounce the advertisements Tuesday.

“This dirty political ad is clearly intended to benefit Professor Elizabeth Warren, and it’s shameful that this campaign has so quickly gone into the gutter,” Barnett said in a statement. “Professor Warren needs to strongly denounce the negative politics behind this ad and call on the League of Conservation Voters to immediately take it down.”

—This story was updated at 11:57 a.m. and 6:24 p.m. Josh Lederman contributed.