The story was originally broken by The Daily Beast.
They quote a letter from the Biden campaign - not Joe Biden personally - , which demands that Giuliani is no longer booked because of the falsehoods and conspiracy theories he spreads. They ask that if he continues to be invited, an "equivalent amount of time" be given to them.
“We write to demand that in service to the facts, you no longer book Rudy Giuliani, a surrogate for Donald Trump who has demonstrated that he will knowingly and willingly lie in order to advance his own narrative,” the letter continues.
The Biden campaign letter goes on to note that “Giuliani is not a public official, and holds no public office that would entitle him to opine on the nation’s airwaves.” And it demands that if the former mayor is put on the airwaves, “an equivalent amount of time” be given “to a surrogate for the Biden campaign.”
The Daily Beast contextualizes this by saying that complaints about bookings are common, while demands are not. They also note that Giuliani "has pushed the bounds in ways few guests have before".
Politico published a copy of the first page of the letter.
The letter was written in September 2019, a time in which Biden held no public office, meaning that it is not a decree, but a request by a campaign which has no legally binding status.