Washington (CNN) - Americans for Prosperity is definitely putting its money where its mouth is.
The conservative non-profit political advocacy group backed by the deep pockets of billionaire industrialists David and Charles Koch announced Wednesday that it will spend around $2.5 million over the next two weeks to run television commercials critical of the federal health care law in four states where Democrats face a challenge in keeping Senate seats in party hands.
The ad buys in Colorado, Louisiana, Michigan and New Hampshire bring to more than $35 million in AFP spending this election cycle on TV spots that highlight how the group says Obamacare has negatively impacted average Americans.
The ads have criticized Democratic senators or Senate candidates for their support of the health care law, and have applauded Republicans opposed to it. AFP's also run Obamacare-related spots in about a dozen or so competitive House races.
The new ads target Democratic Sens. Mary Landrieu of Louisiana, Mark Udall of Colorado, Jeanne Shaheen of New Hampshire, and Rep. Gary Peters of Michigan, who's running this year to keep the seat of retiring Sen. Carl Levin in Democratic hands.
"These politicians are doing a disservice to their constituents when they refuse to acknowledge that Obamacare is leading to canceled plans, higher costs, and lost access to doctors. That's why AFP is continuing aggressive efforts to hold them accountable for their support of Obamacare," said AFP President Tim Phillips in a statement.
The campaigns of the four Democrats were quick to issue statements attacking the new commercials, describing the spots as "misleading"
"Louisianians know better than to believe what they hear from the out-of-state billionaire Koch brothers," said Landrieu's campaign manager, Adam Sullivan.
Shaheen Campaign Manager Mike Vlacich said, "We know the Big Oil Koch Brothers are prepared to spend millions" to try and defeat Shaheen.
"You can't buy a Senate seat here," Vlacich added.
Senate Majority PAC, the leading pro-Democratic outside group that's pushing back against AFP's efforts, says it has spent nearly $9 million this cycle to run spots in support of Democrats and critical of Republicans in key Senate races. Senate Majority PAC says it will continue to fight AFP and other pro-GOP outside groups.
Since the 2010 Supreme Court "Citizens United" ruling opened the floodgates for spending by outside political groups, AFP's been a big spender. In the 2012 election cycle, it dished out more than $33.5 million – a quarter of its entire spending – to run ads urging voters to say no to President Barack Obama.
So far this cycle, AFP's spent far more than any other outside group.
In the past couple of months, Senate Majority Leader Harry Reid has taken to the floor of the Senate to slam the Koch brothers.
The Nevada Democrat has described them as "un-American," having "no conscience" and has said that many of AFP's ads are untrue.