NLRB claims workers need approval to unionize?

This came up in respects to the "unionize college football players" hooray.  The National Labor Relations Board (NLRB) granted permission to the players to form a union.
   Eh?  I thought anyone could form a union.  "Congress shall make no law abridging the right of the people to peaceably assemble... "  First Amendment.  Forming a union, I call that peaceable assembly.  Why should government approval be needed for that?  Of course the Obama people think that government approval is needed for breathing, eating, and drinking. 
   Not that I am in favor of changing college athletes from students who do sports to workers for pay.  What does need to be looked into is the current deal.  Playing sports in return for an all expenses paid degree is a fair deal.  But if the player fails to gain the degree, that's a swindle. I don't know just what the athlete graduation rate is, but if it's less than 95%, heads ought to roll.  Granted, the kinds of kids that go out for football and basketball (jocks we used to call 'em) are not the most promising students.  But with decent guidance, some tutoring, and some serious motivation, they ought to graduate.  "You can't play unless you have a C average" is serious motivation.