Cedar Falls, Iowa — Unite the Country, an independent political action committee supporting Joe Biden, is on pace to outspend his campaign in Iowa with just a week to go before the Iowa caucuses.

The super PAC, which is able to collect unlimited donations, has purchased or reserved more than $4.5 million on broadcast and cable advertisements through Monday, when the Iowa caucuses take place. The Biden campaign is on pace to spend a little less than that, about $4.2 million on television and radio advertisements so far, according to Kantar/CMAG data.

Other major candidates, like Elizabeth Warren and Bernie Sanders, have forsworn and repeatedly criticized super PACs on the campaign trail. They object to the fact that the groups are allowed to raise unlimited amounts of money as long as they do not coordinate with a campaign. Individual donations to political candidates are capped at $2,800 per election (primary and general elections are considered separate). Biden had initially opposed super PACs, but dropped his opposition in the fall.

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Just in the week leading up to the Iowa caucuses, Unite the Country is on pace to spend about $800,000 on advertisements compared to about $467,000 by Biden's campaign. That would put him on similar footing in ad time with Sanders and Warren. This week, Sanders is on track to spend $1.3 million, Warren has placed $1.1 million in ad buys, Amy Klobuchar has so far booked $383,000 in ad buys and entrepeneur Andrew Yang has purchased $188,014 on the airwaves.

The spending from the pro-Biden super PAC comes as polls have shown an incredibly tight race in Iowa with just a week left until the caucuses. The latest CBS News Battleground Tracker showed Sanders leading Iowa with 26%. He was followed by Biden (25%), Buttigieg (22%), Warren (15%) and Klobuchar (7%).

It's not immediately clear how much Buttigieg will be spending in the final week on TV in Iowa.

Businessman Tom Steyer, who has spent $15.8 million on advertisements in Iowa, has reserved $920,000 worth of air time in the final week in Iowa. The richest guy in the race, Mike Bloomberg, has dwarfed the field in ad spending, dropping more than $270 million on ads so far, but he's skipping the early states and focusing his attention on the states that vote on March 3, known as Super Tuesday.

Biden ignored questions from CBS News in Cedar Falls, Iowa on Monday about the super PAC spending in Iowa. He dropped his vocal criticism against super PACs after the Trump campaign pledged to spend millions of dollars against Biden's primary candidacy.

"If that was happening to any other candidate, there would be Democrats responding the same way...to take on Trump," Biden told CBS News at the time.

"I have done nothing — nothing — to cooperate with [the super PAC]," Biden said and pledged that if he's elected, he would try to move toward public funding of elections.

Unite the Country was established in October by several longtime Biden allies and on Friday faces its first required disclosure of its donors, according to Federal Election Commission rules.

"It's going to take more than a special-interest funded TV ad to win the caucus," Sanders campaign manager Faiz Shakir told CBS News. "Nothing will fundamentally change for the working class if candidates continue to solicit funds from millionaires and billionaires into SuperPACs."

The Biden campaign has not responded to CBS News' request for comment.

Iowa voter Barb Dietz, 75, said even though she doesn't like the idea of super PACs, she likes the ads Unite the Country is broadcasting in Iowa. Dietz argued that it's unfair for Biden to have to weather the negative Trump campaign ads and at the same time compete with the self-funded campaigns of Biden's billionaire rivals, Bloomberg and Tom Steyer.

Iowa's first-in-the-nation caucuses will begin the presidential nominating process next Monday. The state's complex rules require candidates to have at least 15% support in most rooms to win delegates, meaning some people will end up supporting their second-choice candidate.