Political spending is a form of protected speech under the First Amendment, and the government may not keep corporations or unions from spending money to support or denounce individual candidates in elections.

-Justice Anthony Kennedy,

Opinion of the Court,

Citizens United v. Federal Elections Commission

What did the Supreme Court decide in the Citizens United case?

Corporations and unions may seek to persuade voters in elections.

Corporations and unions cannot enter into politics.

Freedom of speech is restricted to individuals, not corporations or unions.

The government cannot regulate freedom of speech.

The answer that seems to be the most appropriate one is the first: Corporations and unions may seek to persuade voters in elections.

Federal Law prohibited unions, corporations, and other associations from spending money on ads that supported or went against a particular candidate. That, however, was judged to be in conflict with the Constitution, since the First Amendment concedes free speech to all. Therefore, associations are allowed to produce ads expressing their political opinions and, thus, influencing voters. Such decision is still subject to much discussion and former President Barack Obama has spoken against it, claiming it would open the floodgates for organizations to pursue their own interest.