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.