WASHINGTON -- A slim majority of Supreme Court justices seemed skeptical Tuesday that the federal government may cap the total amount of money that individual donors can give to political candidates running for federal office, in a case that could have a massive impact on the campaign finance system.

In McCutcheon v. Federal Election Commission , the high court is set to decide whether the limits on aggregate federal campaign contributions -- the overall cap currently stands at $123,200 per donor for the 2014 election cycle -- are unconstitutional because they place a burden on the free speech rights of donors.

Shaun McCutcheon, the man bringing the case, only seeks to give the maximum individual donation to more candidates. But Senate Minority Leader Mitch McConnell (R-Ky.) is trying to use the case as a vehicle to persuade the Supreme Court to dismantle contribution limits altogether .

Court observers were keeping a close eye on Chief Justice John Roberts, who most campaign finance reform advocates see as the only hope of upholding the aggregate contribution limits. Roberts joined the majority in a 2006 decision holding that contribution limits were constitutional.

Speaking of the aggregate limits on Tuesday, Roberts said, "It seems to me to be a very direct restriction" on donations that, individually, Congress has decided do not pose a corruption threat.

Solicitor General Donald Verrilli Jr. , representing the FEC, based his argument to uphold the limits on the possibility that a candidate could solicit a check up to $3.5 million for a joint fundraising committee. This solicitation, Verrilli argued, would violate the ban on the solicitation of extremely large contributions that the court upheld in the 2003 McConnell v. FEC case.

Roberts responded, "I appreciate the argument about the $3.5 million check," but he wondered if there was a way to balance the corruption concern around this solicitation with what Roberts saw as the First Amendment burdens of the aggregate limits.

"I suppose you could calculate and set an aggregate limit that is higher," Verrilli answered.

Justice Anthony Kennedy is usually seen as the high court's swing vote between the conservative and liberal blocs, but he wrote the controversial 2010 Citizens United opinion that paved the way for so-called super PACs to dominate election spending. He was not seen as likely to unite with the liberal-leaning justices in the McCutcheon case.

The current case got its legs at the Conservative Political Action Conference in 2012, when McCutcheon, an Alabama business owner, began talking with a conservative election lawyer. McCutcheon didn't like the restrictions placed on the total amount in donations he could make to political candidates, and the lawyer said he could sue to have them changed.

"He could tell I didn't like 'em, so he said we could challenge and it would go all the way to the Supreme Court," McCutcheon told The Huffington Post earlier this year. "I didn't really believe him."

McCutcheon, who recently told The New York Times that Americans "need to spend more money on politics, not less," doesn't take issue with the base limits on the amount of money a contributor can give to an individual politician.

"This is not about base limits, this is about aggregate limits," McCutcheon told HuffPost.

McConnell, however, is aiming straight for the base limits restricting the amount a donor can give a single candidate ($2,600 per election) or a political party committee ($32,400). His argument hinges on overturning the Supreme Court's 1976 ruling in Buckley v. Valeo, which found campaign contribution limits to be constitutional but campaign expenditure limits to be an unconstitutional burden on free speech. McConnell wants to end this distinction and with it the limits on what a donor can give directly to a candidate.

"This is a severe restriction on political speech," Bobby Burchfield , representing McConnell in the case, argued in court Tuesday. The aggregate contribution limits, he said, force candidates and political parties to compete for an "artificially limited pool of money."

Justice Antonin Scalia said that aggregate limits have a "consequence, to sap the vitality of political parties" and encourage "drive-by PACs." He also noted that with the explosion in independent electoral spending, the aggregate limits are not "stopping big money in politics."

As previously pointed out by campaign finance watchdogs, the court could accept McConnell's arguments, but still defer to a future case any direct ruling on the base contribution limits. This is what Campaign Legal Center President Trevor Potter calls the "grenade" in the McCutcheon case.

Even if McConnell doesn't get his way and the court issues only a narrower decision that does away with aggregate contribution limits, good-government advocates warn that such a ruling would create a more corrupt elections process.

Joint fundraising committees already streamline contributions from large donors, who write a single check that is then distributed to various candidate campaigns, political party committees and congressional leadership PACs. Through the joint committees, congressional leaders and presidential candidates use their greater fundraising capabilities to support others in their party. A lack of aggregate contribution limits would free, say, House Speaker John Boehner (R-Ohio) to accept a $2.5 million donation that could be distributed to Republican candidates in each of the 435 House districts as well as the national GOP committees.

The justices will issue their opinion in McCutcheon before the end of June.