Justice Stephen Breyer, writing for the liberal dissenters, said that the court's conservatives had "eviscerated our nation's campaign finance laws" through Wednesday's ruling and the Citizens United case.
"If the court in Citizens United opened a door, today's decision we fear will open a floodgate," Breyer said in comments from the bench. "It understates the importance of protecting the political integrity of our governmental institution. It creates, we think, a loophole that will allow a single individual to contribute millions of dollars to a political party or to a candidate's campaign."
Roberts said the dissenters' fears were overstated because other federal laws prohibit the circumvention of the individual limits and big donors are more likely to spend a lot of money independently in support of a favored candidate.
Reaction to the ruling generally followed party lines, with advocates of capping money in politics aligned with Democrats in opposition to the decision.
Republican National Committee Chairman Reince Priebus called the Supreme Court decision "an important first step toward restoring the voice of candidates and party committees and a vindication for all those who support robust, transparent political discourse."
The GOP and Senate Republican Leader Mitch McConnell of Kentucky had argued that other decisions relaxing campaign finance rules had diminished the influence of political parties.
Democratic Sen. Chuck Schumer of New York said, "This in itself is a small step, but another step on the road to ruination. It could lead to interpretations of the law that would result in the end of any fairness in the political system as we know it."
Congress enacted the limits in the wake of Watergate-era abuses to discourage big contributors from trying to buy legislative votes with their donations and to restore public confidence in the campaign finance system.