TDA and Etrade have different parameters for what makes them require calling in. Usually TDA is the problem when trading pennies. They restrict way more OTC stocks than ET.

ET seems to be the only house with this call in requirement for UNVC, so IMO there's either a new situation causing ET to proceed differently, or an old situation that got new light shed onto it by all the recent attention. Either way though, it's got to do with the shell, and how ET allocates new shares....I think. When I think about why a brokerage would do such a thing, it seems like the cause would be related to the task of moving shares back and forth.

IDK all the reasons that would make moving shares back and forth difficult, but I'm sure some are bad and some are not bad at all.