A divided U.S. Supreme Court struck down decades-old restrictions on corporate campaign spending, reversing two of its precedents and freeing companies to conduct advertising campaigns that explicitly try to sway voters.

The 5-4 majority, invoking the Constitution's free-speech clause, said the government lacks a legitimate basis to restrict independent campaign expenditures by companies. The ruling went well beyond the circumstances in the case before the justices, a dispute over a documentary film attacking then-presidential candidate Hillary Clinton.

"When government seeks to use its full power, including the criminal law, to command where a person may get his or her information or what distrusted source he or she may not hear, it uses censorship to control thought," Justice Anthony Kennedy wrote for the majority. "This is unlawful. The First Amendment confirms the freedom to think for ourselves."

Companies, which had been barred since 1947 from using general-treasury dollars in support of or in opposition to a candidate, now can spend millions of dollars on their own campaign ads, potentially punishing or rewarding lawmakers for their votes on legislation. Labor unions, though they weren't directly at issue in the case, have been subject to the same restrictions and may also now expand their political spending.