The group, which is by far making the largest independent expenditure in the race, announced on Wednesday a $200,000 mail program that charges Brown is in the pocket of Big Oil and has not supported global-warming regulations. The group has spent $1 million so far this year seeking to defeat Brown and more than $2 million this cycle on issue ads critical of Brown's record.
Brown and his Democratic challenger, Elizabeth Warren, are in a tight race: A number of recent polls have showed Warren with a slight lead, and a poll released Tuesday had Brown edging her out. They face off in the third debate of the election season Wednesday night.
Brown and Warren agreed to a "people's pledge" that bans third-party advertising on TV, radio, and the Internet. But that pledge does not include get-out-the-vote efforts and direct mail, which is how LCV hopes to influence voters.
"Despite the candidates' pledge on how we can spend in this race, our program in the mail and at the door will help us have a substantial impact on this race," said LCV's Navin Nayak.
LCV has already spent more than $3 million so far in advertising against Brown in the last two years. Close behind it is its ally, the League of Women Voters, which has spent almost $1.2 million. Combined, these two groups are spending double what Republican groups such as the Karl Rove-founded American Crossroads GPS are spending to defend Brown.
Crossroads GPS, which is one of only two conservative groups spending any money on the Massachusetts Senate race, has spent $1.1 million. In late September, the group began "robo-calling" voters with anti-Warren messages, according to a Boston Globe article. (The other GOP-leaning group spending money in this race, the Coalition for American Jobs, has spent less than $500,000).
Nayak said the candidates' ban on outside advertising has limited Crossroads' influence on the race.
"I think it underscores that a lot of what Crossroads does is a one-tricky pony," Nayak said Wednesday. "They put up TV ads...I have not seen any other activity from them in any other shape or form."
A request for comment to Crossroads was not immediately returned. Crossroads has spent $42 million on Senate races so far this cycle.
LCV has played in other Senate races, including efforts in Montana and New Mexico. On Tuesday, it announced a $300,000 mail program in Connecticut to defeat Republican Senate candidate Linda McMahon.
Josh Kraushaar contributed.