Colbert recently spent a day as a vegetable picker on a farm in upstate New York, participating in the United Farm Workers' Take Our Jobs campaign. The program has offered citizens and legal residents jobs as field laborers working alongside thousands of other farm workers, most of whom are undocumented.
The challenge, meant to counter the idea that illegal immigrants are taking jobs Americans would do, is being featured this week on Colbert's show "The Colbert Report."
"He'll talk about what he learned, why he did it and what's important to do for farm workers," an aide for a Democratic member of the committee familiar with Colbert's testimony told ABC News.
Colbert said on "Good Morning America" Thursday he's excited about his trip to the Hill. "The main reason I'm testifying before Congress is to get that CSPAN 1 bump for my ratings," he said. "I hope it's CSPAN 1. If it's CSPAN 2, I've been lied to."
Republicans on the committee, however, say they don't find Colbert's appearance a laughing matter.
"What a joke," tweeted Utah Republican Jason Chaffetz Wednesday. "All the serious issues, and we have Colbert as an 'expert.' I am a fan of Colbert, but immigration expert???"
Chaffetz, who has appeared on Colbert's show, told ABC News he'll give Colbert the benefit of the doubt and ask him serious questions about his farm experience but said he does not believe the testimony will be substantive.
"It'll be entertaining," Chaffetz said. "He's the best fake newscaster in the country, and it's fitting for this fake hearing to have Colbert."
Other Republicans have speculated as to whether Colbert will testify in character and whether that would make a mockery of congressional testimony that is given under oath. It's unclear what recourse they might have to lodge a complaint.
Colbert's appearance certainly won't be the first time a celebrity has testified as an expert before Congress. Actor Kevin Costner was on the Hill Wednesday to lobby Congress for an $895 million Gulf oil spill relief bill, and Actress Mariska Hargitay, who plays a sex crimes detective on "Law & Order," testified about rape prevention in May.
UFW president Arturo Rodriguez appeared on Colbert's show in July and invited the comedian to experience the life of an immigrant farm worker firsthand.
More than three million people have visited the Take Our Jobs Web site and 8,600 expressed interest in the farm jobs, according to the UFW. But only seven have actually accepted the offer.
"Why do you think so few Americans have taken up this challenge?" Colbert asked Democratic Rep. Zoe Lofgren, who chairs the House Judiciary subcommittee on immigration , and who went with Colbert to the farm.
"It's tough, dirty work," said Lofgren. "It's hot."
"You're saying Americans aren't tough, madam?" he replied. "Are you saying Americans are pussies?"
"I'd never say Americans are pussies," said Lofgren. "Sixteen Americans have shown up. Perhaps it will be an example and two million Americans will show up."