A leading Maryland environmental group has taken the unusual step of publicly committing $40,000 to the defeat of a Prince George's County senator it sees as being too pale a shade of green.

The Maryland League of Conservation Voters announced it would spend that money to oust Sen. C. Anthony Muse, a Democrat, in the June 24 primary. The league has endorsed Del. Veronica Turner, who is challenging Muse for the party nomination.

The organization pointed to Turner's lifetime score of 92 percent on its legislative ratings, compared with Muse's 65 percent -- low for a Democrat from Prince George's. The league specifically called Muse out for his opposition to Gov. Martin O'Malley's bill encouraging the development of an offshore wind power industry. Muse was part of a committee majority that blocked the legislation in 2011 and 2012 before Senate President Thomas V. Mike Miller changed his panel assignment. The legislation passed in 2013.

Muse's voice mail was full, preventing a reporter from leaving a message requesting comment.

It is not rare for an organization to target a lawmaker who has opposed its agenda and who appears vulnerable to a challenge. What is unusual is the league's public announcement of its plan to target a specific lawmaker, who can be expected to have a long memory if re-elected.

The league's executive director, Karla Raettig, called the group's commitment of $40,000 "our largest political campaign investment in our more than 30-year history."

In a state Senate campaign, $40,000 represents a significant intervention. It is more than twice the $19,000 Turner herself has on hand, and almost half the $90,000 Muse has in the bank.

Jen Brock-Cancellieri, a spokeswoman for the league, said the sum makes up the majority of its political spending this year.

"We wanted to go all in to show there's political consequences to blocking action on climate change," she said.