MANCHESTER, N.H. — An independent political committee supportive of Newt Gingrich plans to release a film critical of Mitt Romney's tenure at a private-equity firm, days after a Las Vegas billionaire contributed $5 million to the group to bolster the former House speaker's White House run.

The Gingrich-leaning Winning Our Future PAC said Sunday that the 28-minute video — which assails Romney for "reaping massive awards" while head of Bain Capital — will be posted online soon and could show up on TV just as the GOP primary season heats up.

Both the film and the large contribution highlight the growing role that new "super" political-action committees are playing this election.

Just weeks ago, a Romney-leaning super PAC called Restore Our Future hammered Gingrich with $3 million in negative ads that largely contributed to the former speaker's eroding support before the Iowa caucuses.

Gingrich finished in fourth place.

Now, the tables have turned: Winning Our Future's case marks the first time Gingrich and his allies have targeted Romney's time at Bain.

Bain has been credited with turning around dozens of companies, including well-known brands such as Domino's Pizza, but its record has been criticized — notably by the Democratic National Committee — for slashing jobs in the process.

The film is called "When Mitt Romney Came To Town."

A person familiar with the development said Sheldon Adelson, a casino mogul and longtime donor to Republican candidates, made the $5 million contribution Friday to Winning Our Future, which is run by Gingrich allies.

The person, who was not authorized to discuss the matter publicly, said Adelson is expected to contribute to groups backing the Republican nominee, be it Gingrich or one of his rivals.

The movie includes emotional interviews with people who lost jobs at companies that Bain bought and later sold.

"We had to load up the U-Haul because we done lost our home," one woman says.

Democrats have signaled they intend to make Romney's history at Bain a key part of their case against him if he wins the Republican presidential nomination.

But Bain has also emerged as an issue in the Republican contest, despite the party's pro-free market stance and business-friendly policies, reflecting the depth of public anger about the economy.

At an appearance Sunday in New Hampshire, Gingrich suggested that Bain's approach was to carry out "clever legal ways to loot a company."

Super PACs have sprouted up from a series of federal court rulings, including the Supreme Court's Citizens United case in 2010 that stripped away restrictions on corporate and union spending in elections.

The groups can't coordinate directly with campaigns, but many of them active in this election are staffed by longtime supporters of the candidates.

While some super PACs must disclose their contributors' names later this month, many will never be known.

Some super PACs have established nonprofit arms that are permitted to shield contributors' identities as long as they spend no more than 50 percent of their money on electoral politics.

Crossroads, the giant conservative outfit tied to former George W. Bush political adviser Karl Rove, operates both a super PAC, Crossroads GPS, and a nonprofit, American Crossroads.

Crossroads GPS and other Republican-leaning super PACs played a significant role in the 2010 midterm elections, helping deliver the House to the GOP and boost the number of Republicans in the Senate.

The 2012 contest is the first to test the influence of such groups in presidential politics.

No candidate has seen his fortunes affected by the emergence of super PACs more than Gingrich.

Riding high in polls just a month ago, he became the target of a $3 million advertising barrage sponsored by Restore Our Future, a super PAC supporting Mitt Romney run by several of the former Massachusetts governor's allies.

The ads, which pounded Gingrich for his ties to federal housing giant Freddie Mac and his reversal on issues such as climate change, sent his political fortunes plunging in Iowa.

Romney and Gingrich tangled over the role of super PACs in a nationally televised debate Sunday. Romney said he had not seen Restore Our Future's ads but defended their content.

"Governor, I wish you would calmly and directly state it is your former staff running the PAC," Gingrich said to Romney, warning his own allies would be on the air soon.

Gingrich is hoping to resuscitate his campaign in the South Carolina primary Jan. 21. With Romney heavily favored to win the New Hampshire primary Tuesday, his rivals are looking to slow his momentum when the contest moves to the South.

Several super PACs have already played a role in the Republican campaign.

They include Make Us Great Again, a super PAC backing Texas Gov. Rick Perry; Our Destiny, supporting former Utah Gov. Jon Huntsman; and the Red White and Blue Fund, which helped revive former Pennsylvania Sen. Rick Santorum's campaign in Iowa and is running ads in South Carolina.

Information from The New York Times is included in this report.