WASHINGTON (AP) — The U.S. Chamber of Commerce is launching ads in Florida, Missouri, Hawaii and Ohio as Democrats struggle to hold Senate seats and their slim majority. The Republican-friendly lobbying group is also targeting 17 House races from New York to Minnesota.

The ads, hitting Democratic incumbents over votes for President Barack Obama's health care overhaul and backing his energy policies, will begin airing Wednesday and Thursday and run for 10 days to two weeks, part of a multimillion-dollar buy six months before the election. The ads in House races will focus on contests in New York, Illinois, Michigan, Minnesota, Ohio, Rhode Island, Florida and Georgia.

The entry into markets in Democratic-leaning New York, Rhode Island and Hawaii represents a significant commitment from the GOP-allied chamber as Republicans try to capture control of the Senate and hold onto their majority in the House.

"We're going to play in every corner of this country," Rob Engstrom, the national political director for the chamber, said Tuesday in an interview.

The chamber declined to say how much it will spend in this round of advertising. Ad buys earlier this year in eight Senate races and 12 House races was estimated at $10 million.

In Missouri, first-term Sen. Claire McCaskill is considered one of the most vulnerable Democrats. The chamber, which ran ads against her earlier this year, has bought time for a spot that criticizes her votes for health care and ends with the tagline, "Claire McCaskill: More government, more Washington, less opportunity, less growth."

McCaskill has criticized the outside groups that have filled the airwaves in her state and around the country after the Supreme Court's decision in the 2010 Citizens United case, which erased many campaign-finance regulations.

In Florida, two-term Democratic Sen. Bill Nelson has raised more than $9 million while his Republican foes, Rep. Connie Mack and former Sen. George LeMieux, have struggled in attracting significant donations for a state with 10 major media markets, including expensive Miami. The chamber advertising is certain to fill in the gap for the GOP which won't settle on a nominee to challenge Nelson until Aug. 14.

The chamber ad complains about Nelson's health care vote.

"Obamacare will be a nightmare for seniors," the ad says. "Did Bill Nelson consider the consequences when he cast the deciding vote for Obamacare? ... Call Bill Nelson and tell him to support the repeal of Obamacare."

A Quinnipiac poll last week found that by a 51-38 percent margin, Florida voters want the Supreme Court to overturn the health care law.

Mark Wilson, president of Florida's Chamber of Commerce, said they welcome the U.S. Chamber's effort in the state six months before the election as the local chamber doesn't get involved in congressional races.

"We know that this election is going to be about the future of our country," Wilson said. "There's a group of candidates who want us to be more like France, and there's a group of candidates that want us to be more like free enterprise and like the United States used to be."

In New York, the U.S. Chamber is running ads criticizing Democratic Reps. Tim Bishop, Bill Owens, Louise Slaughter and Kathy Hochul. It's running spots praising Republican Reps. Nan Hayworth, Ann Marie Buerkle and Chris Gibson, who face tough contests this November.

"We're going to be going on offense, as well as protecting our friends in this round," said Engstrom.

In Rhode Island's 1st Congressional District, the chamber is running an ad promoting Brendan Doherty, a challenger to first-term Democratic Rep. David Cicilline.

"Rhode Island is hurting," the ad says. "Brendan Doherty wants to get Rhode Island back on track. This lawman has a plan."

The lone Democrat getting a boost from the chamber is conservative Rep. John Barrow in Georgia.

"We're running a sustained campaign between now and November," Engstrom said. "This is now the largest campaign in the history of the U.S. Chamber."

Democrats hold a 51-47 majority in the Senate plus two independents who caucus with the Democrats. In the House, Republicans' advantage is 242-190 with three vacancies.

In Ohio, a presidential battleground state, Democratic Sen. Sherrod Brown is facing a spirited challenge from Republican state treasurer Josh Mandel. In Hawaii, Republicans are hoping former Gov. Linda Lingle can break the Democratic grip on the Senate seat; incumbent Daniel Akaka is retiring.

Earlier this year, the chamber ran ads in eight Senate races — Ohio, Montana, Wisconsin, Virginia, Indiana, Hawaii, Missouri and North Dakota — and 12 House races that hit more than 40 media markets, including the expensive Washington region. Republicans and Democrats estimated the buy at $10 million; the chamber would only say eight figures but did describe the effort as unprecedented in its 100-year history.