BOSTON — Spending by outside groups in Massachusetts’ special U.S. Senate election has topped $1.25 million, with the largest amount going to support Democratic candidate Edward Markey.
The biggest spender in the race so far is the League of Conservation Voters, a national environmental advocacy group based in Washington, D.C. The group has already reported pumping more than $545,000 into its efforts to help elect Markey, according to an Associated Press review of reports filed with the Federal Election Commission.
Markey is facing off against fellow U.S. Rep. Stephen Lynch in the Democratic primary on April 30.
The league’s money has been spent on staff time, press releases, recruitment of volunteers, office supplies, political bumper stickers, rally signs, field campaign consulting, pledge cards and repairs to digital tracking equipment.
The group announced last month that it planned to spend at least $650,000 on a field campaign to support Markey, including knocking on the doors of more than 240,000 likely Democratic primary voters.
‘‘Our field campaign is resonating with voters across Massachusetts,’’ said Navin Nayak, the league’s senior vice president of campaigns.
The group said it is targeting many of the same neighborhoods it visited last year when it supported then-Democratic U.S. Senate candidate Elizabeth Warren, who went on to defeat Republican Sen. Scott Brown in the November election.
Markey has made environmental issues one of his top priorities and the focus of a television campaign ad that highlighted his role in holding BP responsible for the 2010 oil spill in the Gulf of Mexico.
The group making the biggest push on behalf of Lynch is the International Association of Firefighters, which has reported spending more than $85,300, including money for gas, tolls, rally signs, car rentals and travel expenses. Lynch worked as an ironworker for 18 years and, along with Markey, has appealed to unions for their support.
Another group spending big to help defeat Lynch is the NextGen Committee, which has reported spending more than $196,000.
The group is backed by California billionaire Thomas Steyer, who has called on Lynch to oppose the Keystone XL Pipeline, which would run from western Canada to Texas. Opponents say it poses an environmental risk, but supporters say it will create needed jobs.
Among the group’s expenses was $54,700 for aerial banners. The group paid to have an airplane trail a banner that read: ‘‘Steve Lynch says: Go Habs! And Go Canadian Dirty Oil.’’
Lynch, who has criticized Steyer for spending money in the primary race, said the banner was meant to question his loyalty to the Boston Bruins. The ‘‘Habs’’ is the nickname for the Montreal Canadiens. The banner was flown over downtown Boston ahead of matchup between the two hockey teams.
Lynch’s campaign said he’s not only a longtime Bruins fan, but he sponsored legislation creating the Boston Bruins license plates that help raise money for youth hockey in Massachusetts.
The NextGen Committee also spent more than $50,000 for video mobile billboards and $40,000 for online advertisements.
That’s an apparent violation of an agreement signed by Lynch and Markey known as the ‘‘People’s Pledge,’’ which is designed to discourage radio, television and Internet ads by outside groups. The deal also applies to political mailings.
If there is a violation, the candidate who benefits agrees to pay half the cost of the ad to a charity named by their rival.
Markey’s campaign said it would make a donation to a charity chosen by Lynch.
Another big supporter of Markey is SEIU, the Service Employees International Union, which has made more than $368,000 in independent expenditures to help elect him. The money went to cover gas, staff salaries and canvassing services.
Other groups that have reported making independent expenditures on behalf of Markey is the abortion rights group NARAL Pro-Choice America and the environmental advocacy group 350.org Action Fund.
Markey says he is a supporter of abortion rights. Lynch says he is personally opposed to abortion, citing his Catholic faith, but he has emphasized during the campaign that if elected to the Senate, he would not vote to make abortion illegal.
None of the independent expenditures reported to the FEC by the end of the week were made to either support or oppose the three Republican U.S. Senate candidates — former U.S. Attorney Michael Sullivan, Norfolk state Rep. Daniel Winslow and Cohasset businessman Gabriel Gomez.
The Tea Party-aligned Conservative Campaign Committee, however, has said it plans to spend up to $200,000 on radio and television ads to support Sullivan and target Winslow and Gomez.
Winslow and Gomez have called on Sullivan to renounce the ads by the group, which they say holds extreme anti-gay positions. The radio ads the group recorded criticize Winslow and Gomez, but make no references to gay issues. Sullivan has said he’s not familiar with the group.
The three Republican candidates have not agreed to the ‘‘People’s Pledge.’’ They note that Lynch and Markey began the campaign with hefty stockpiles of money.
The independent expenditures by outside groups give no indication how much each candidate has raised in donations so far. The first reporting filing deadline in the race is April 18, less than two weeks before the primary.
The special election to fill the seat left vacant by the resignation of John Kerry to become secretary of state is June 25.