“The government may regulate corporate political speech through disclaimer and disclosure requirements, but it may not suppress that speech altogether,” Justice Anthony Kennedy wrote in the 5-4 majority decision supported by Chief Justice John Roberts and Justices Samuel Alito, Clarence Thomas and Antonin Scalia.

Justice John Paul Stevens noted in his dissent that “the majority’s approach to corporate electioneering marks a dramatic break from his past. ... Relying largely on individual dissenting opinions, the majority blazes through our precedents, overruling or disavowing a body of case law.”

“It essentially does away with the restrictions on independent expenditures—it’s breathtaking, the scope of this and the implications it will have on political campaigns,” said Mary Streett, a partner at Mayer Brown who was still reading through the opinion Thursday morning. “This opinion is far reaching and will change the way corporations can get involved in political campaigns.”