Chamber expands Senate ad blitz to five more states

This is the latest volley from the group. It spent a combined $1.4 million on Senate races in Hawaii, Nevada, New Mexico and North Dakota earlier this month.

The ads hit Democratic Sens. Bill NelsonBill NelsonThree more Republican senators to meet with Supreme Court nominee This week: Congress on track to miss Puerto Rico deadline Senate looks for easy wins amid 2016 gridlock MORE (Fla.), Jon TesterJon TesterElizabeth Warren stumps, raises funds for Duckworth Senators subpoena EPA officials over mine waste spill The Hill's 12:30 Report MORE (Mont.), and Sherrod BrownSherrod BrownLawmaker offers bill to impose 'exit tax' on expatriating companies For Clinton, there's really only one choice for veep Let the Democratic veepstakes begin MORE (Ohio) as well as Rep. Tammy BaldwinTammy BaldwinThe Trail 2016: The campaign that never sleeps Dem senator: 'I am a human being and a superdelegate’ Senate Dems press McConnell, GOP on Supreme Court MORE (D-Wis.) for backing the Democratic health insurance reform law, and slam Rep. Martin HeinrichMartin HeinrichCarter pledges probe of sex assault testimony Week ahead: Rival encryption efforts clash on Capitol Hill Encryption commission bill picks up more backers MORE (D-N.M.) for opposing expanded drilling for oil and immediately building the Keystone XL pipeline.

The group does not disclose how much it spends on ads and did not respond to a request for comment on this ad buy.

The Democratic Senatorial Campaign Committee fired back, accusing the Chamber of spending "secret money" to prop up "weal candidates."

"These Republican candidates would be nothing more than a rubber stamp for the Chamber’s special interest agenda that puts insurance companies over seniors, oil companies over small businesses, and billionaires over the middle class," said DSCC spokesman Matt Caner. "As voters learn more about the Republicans' special interest agenda, they'll quickly realize how wrong these priorities are for their families and our country."

Watch the ad against Heinrich:

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