CBS's Face the Nation booked 3 Republicans and 0 Democrats on Sunday's show

[Slammer]

16. administration

For the official stance of the administration, the show makes a request of the White House and they assign someone to make the appearance. Usually it's someone with some expertise on the issues of the day and the higher the profile of the show, the bigger name/office of the person who is assigned to appear.

For congressmen and senators, they can contact their offices directly if there's someone specifically they want on the program. Or if the program doesn't have anyone in particular in mind, they can contact the leadership of whichever party and ask them to find a volunteer.

I highly doubt the administration refused to send a representative to Face the Nation. Completely snubbing a show is usually only done if the network or show has behaved in a particularly obnoxious manner and the administration is wanting to send a message to the news industry.