After three presidential debates and one vice-presidential debate between the Democratic incumbents and their Republican challengers, the third-party candidates are finally getting their national forum.

On Tuesday at 8:55 p.m. (EST), a televised debate among four third-party candidates will be moderated by longtime talk-show host Larry King.

Presidential nominees Jill Stein (Green Party), Gary Johnson (Libertarian Party), Virgil Goode (Constitution Party) and Rocky Anderson (Justice Party) will participate.

Twitter users are encouraged to use the hashtag #AskEmThisLarry to propose debate questions for King to pose to the third-party candidates.

The last third-party candidate to face Democratic and Republican nominees in a televised debate was independent Ross Perot in 1992.

The Commission on Presidential Debates, which sponsors debates between the major-party candidates (including this year's forums with Barack Obama and Mitt Romney), requires that a candidate be averaging at least 15 percent in national polls to be included.

Third-party candidates complain that's a hurdle that's almost impossible to clear before voters have a chance to hear their views.

"This commission exists for the principal purpose of protecting and strengthening the two parties," George Farah of Open Debates, a group that advocates changing the debate system, told NPR.

Stein was arrested outside this year's second presidential debate at Hofstra University after she attempted to enter the debate, calling it a "mockery of democracy," according to The Huffington Post. Johnson filed a lawsuit against the Commission in September, arguing that he'd been unfairly excluded from debating.

The debate at the Hilton Chicago is sponsored by the nonprofit Free & Equal Elections and will be telecast on the CSPAN channel, Al Jazeera and LINK TV and streamed at www.freeandequal.org/live and cspan.org, according to Free and Equal.

Are third-party candidates relevant in this year's presidential election? Would you vote for one? Tell us in the comments.