[meyer]

On what grounds can they prevent a reporter from doing their job (assuming public property, etc.)?

[Pontiac]

an NPR contributor, reported that campaign staffers prevented him from interviewing voters outside a rally featuring Michelle Obama.

I can understand that the campaign can place restrictions on reporters inside a campaign venue but outside I would tell them that these people and I are outside of the event, on public property and we are free to converse if we so choose, now kindly go pound sand.

Of course the event workers could then retaliate against the reporter and refuse him entrance but that would make for a very nice NPR story.