A liberal action group is spending big this week against three Republican senators over their vote seeking to cancel Environmental Protection Agency (EPA) regulation of greenhouse gases.

The group Americans United for Change (AUFC) is spending over $400,000 on television ads in the home states of Sens. Chuck GrassleyCharles (Chuck) Ernest GrassleyGOP senators eager for Romney to join them Five hurdles to a big DACA and border deal Grand jury indicts Maryland executive in Uranium One deal: report MORE (R-Iowa), Richard BurrRichard Mauze BurrNSA spying program overcomes key Senate hurdle Senate Intel chairman: No need for committee to interview Bannon McConnell: Russia probe must stay bipartisan to be credible MORE (R-N.C.) and Scott Brown (R-Mass.), hammering them for joining with fellow Republicans to support a resolution of disapproval last week seeking to nix new EPA rules.

The ads are "hitting these senators hard on the nose for this vote in an effort to make it as politically toxic as possible for them back home to continue standing with Big Oil," said a spokesman for the group.

The three Republicans — Burr and Grassley face reelection battles this year, while Brown will almost surely face a tough challenge in 2012 — joined all other GOP senators and six Democrats in a failed procedural vote seeking to cancel EPA rules reining in emissions contributing to global warming.

AUFC will spend $118,000 to run an ad against Grassley in Des Moines and Cedar Rapids, and $234,000 to run an ad against Burr in Raleigh and Charlotte. Those spots will run June 15-21. The group also already spent $53,000 to run its ad against Brown, a spot that aired during Sunday night's NBA finals game between the Los Angeles Lakers and Boston Celtics.

The ads are also part of a sustained campaign by the liberal group to pressure Republicans on their vote over the resolution, tying the GOP senators' vote to the ongoing oil spill in the Gulf of Mexico, as well as to the progress of a potential energy and climate bill through Congress this year.

Find an example of the ads, the Brown ad, below: