The justices said in a 5-4 vote that Americans have a right to give the legal maximum to candidates for Congress and president, as well as to parties and PACs, without worrying that they will violate the law when they bump up against a limit on all contributions, set at USD 123,200 for 2013 and 2014.
That includes a separate USD 48,600 cap on contributions to candidates.
But their decision does not undermine limits on individual contributions to candidates for president or Congress, now USD 2,600 an election.
The overall limits "intrude without justification on a citizen's ability to exercise 'the most fundamental First Amendment activities,'" Roberts said, referring to the US Constitution and quoting from the court's seminal 1976 campaign finance ruling in Buckley v. Valeo.
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Justice Stephen Breyer, writing for the liberal dissenters, took the unusual step of reading a summary of his opinion from the bench.
Congress enacted the limits in the wake of 1970s abuses to discourage big contributors from trying to buy votes with their donations and to restore public confidence in the campaign finance system.
Most notably, in 2010, the court divided 5 to 4 in the Citizens United case to free corporations and labor unions to spend as much as they wish on campaign advocacy, as long as it is independent of candidates and their campaigns.
That decision did not affect contribution limits to individual candidates, political parties and political action committees.