The political arm of a top environmental group plans to spend $485,000 attacking Republican Pennsylvania Sen. Pat Toomey in his re-election fight.

The League of Conservation Voters Action Fund announced Monday its latest ad buy as a part of a $1.5 million ad campaign against Toomey. The fund is partnering with Environmental Defense Action Fund on the campaign.

The environmental groups are backing Democrat Katie McGinty in the Pennsylvania Senate race. McGinty leads Toomey 42.7 percent to 41.4 percent, according to the RealClearPolitics average of polls.

"Voters have been learning a lot about Pat Toomey, and they have realized he just isn't on their side, evidenced by the millions Big Oil polluters have spent to prop up his campaign – and his steadfast defense of the nearly $24 billion they receive in taxpayer handouts," said Clay Schroers, LCV Victory Fund Campaigns director.

"Toomey has been fighting to protect polluter profits in Washington, opposing investments in clean energy and jeopardizing the health of our families by attacking clean air and water protections. Fortunately, Pennsylvanians have a choice in this election, with Katie McGinty committing to putting families first and working to build the clean energy economy that will create new, high-quality jobs in their backyard."

The ad campaign begins Monday and will run for one week on broadcast and cable networks in the Philadelphia area.

The ad will detail Toomey's votes on tax breaks for oil companies, which total about $24 billion, according to the group. The ad also will charge that Toomey has received $700,000 in donations from oil companies during his time in office.

The ad previously ran in the Keystone State in July.

The League of Conservation Voters and the Victory Fund's have spent a combined $5.7 million on four Senate races.