Guess who's not coming to the next Senate debate?

Four U.S. Senate candidates are expected to debate Friday night at UNC Charlotte. And none of them are named Kay Hagan or Thom Tillis.

Libertarian candidate Sean Haugh and three write-in candidates will appear at what's billed as an "all inclusive" debate sponsored by a group called Free the Vote North Carolina.

Hagan and Tillis were invited. Organizers never heard from Hagan; Tillis claimed a scheduling conflict.

It will be the second debate appearance for Haugh, who stood alongside the majority party candidates in Wilmington last week. It will be the first for write-in candidates Barry Gurney, John Rhodes and David Waddell.

Organizers say the debate is to show voters all their choices. That's what elections should be about, says Brian Irving, a spokesman for the Libertarian Party. "We have a democracy," he says, "All the choices available to (voters) should be allowed to speak.”

The event is trying to make a statement about a system that not only keeps some candidates out of debates but often off the ballot.

Some debate organizers, including media organizations, require a candidate to hit a certain polling number to participate. And North Carolina's ballot is notoriously hard to get on.

To get on the ballot, for example, a new political party or unaffiliated candidate has to submit petitions signed by 2 percent of the total number of votes cast in the last gubernatorial election. Now that's 89,366.

Last year a bi-partisan group of state House lawmakers introduced the Voter Freedom Act of 2013, a measure that would have launched a study of ways to ease ballot access. It passed the House 109-5 but went to the Senate Rules Committee where it died.