If they ever set up in Grand Central proper, I believe the NYC and suburban commuters would demand no access to any religion. Port Authoriity and Penn Station are so ugly and present a yucky experience. Sadly, I no longer recall all the First Amendment public forum rules. They belong on the subway level!
I do know there are big problems with the Hare Krishnas. Once during Christmas season, I took a 6th Avenue line. All of a sudden about ten Santa Clauses entertained the train, ringing their bells, and demanding money for charity. I knew who they were. In fact, to altert others I demanded loudly to see theri charity collection permits from the New York State Attorney General. When they were not produced, I loudly proclaimed, you are a fraud. You are illegal. Every charity must be regisitered with the Attorney-Generals Office. Half of the train gave them generous amounts of money. They promptly ran off the train at the next stop. One woman turned to her friend and was furious. "How could you give them money?" "You know who they are?" "Hare Krishnas in disguise." Her friend started crying. She had no idea.
The Hare Krishnas make the Witnesses so main stream. I told the Transit Police what happened. If they want to wear orange robes and chant, that is a religious right. They were not the Salvation Army. New Yorkers are very gullible despite our vaunted sophistication. A gf worked in the U.S. Attorney's Office on federal land fraud cases. New York was targetted in documents for being a great place to find suckers.