I love it when "conservatives" get all worked up about unions being an undefeatable boogeyman when unions get outspent 20-1 by the Koch bros and their sock puppets- Heritage Foundation et al.
Y'all are Goliath whining about David bothering to show up with a slingshot.
Going with the OP, let's say the Court actually ruled on the merits of the case.
BCRA forbids corporations or unions sponsoring ads mentioning a candidate
30 days before a primary or 60 days before a general election.
Before or after that period, they can air anything they want.
A lower court US District Court for DC considered the film Hillary:The Movie CU wanted to show during that stand-off period to be a political hatchet job designed to sway an election, not just a commercial film protected by the First Amendment.
Basically the CU vs FEC case was of two parts: arguing whether CU could show the film (pretty much a slam dunk- let 'em show it) but the real meat of it was challenging Austin vs Michigan Chamber of Commerce allowing unions free rein but limiting corporations' ability to spend on campaigns.
However, before this dust-up corporations were free to form and contribute to PACs. This decision just removes the fig leaf of PACs and allows corporations to directly contribute unlimited amounts of money anonymously.
You can say that the unions and other non-profit organizations liberal, libertarian or otherwise lobbying Congress can go nuts, too but as I said, it's a slingshot vs Goliath funding fight.
IF the Supremes upheld the District Court's decision to make CU wait to show the film corporations still have tremendous influence on the Hill. In a way, it preserves some restrictions on corporate behavior.