The Marvin Gaye vs Robin Thicke case set a precedent and opened up the flood gates, after all, if you can say they're musically similar and win, you can pretty much put any similar sounding songs against each other.
Utpown Funk had 4 more writers added after it was pointed out that The Gap Band's "Oops Upside Your Head" was kind of similar to the small section of vocal at 2:54
youtu.be/OPf0YbXqDm0?t=2m54s
It's a free for all.