ABC News’ Devin Dwyer reports: With left-leaning comedian and satirist Stephen Colbert headed to Capitol Hill tomorrow, some Republican lawmakers are asking whether his appearance will be anything more than a political stunt. Colbert is listed as an expert witness for a House Judiciary subcommittee on immigration, refugees, and border security hearing on immigrant farm workers and the AgJOBS bill. “He’s the best fake newscaster in the country, and it’s fitting for this fake hearing to have Colbert,” said Utah Republican Rep. Jason Chaffetz. “He’s a nice guy and a darn good leg wrestler… But he’s not an expert on farm workers.” Democrat Rep. Zoe Lofgren, the subcommittee chairwoman, invited Colbert to appear after she joined him at a farm in upstate New York in August when he spent a day picking vegetables alongside other migrant workers as part of the United Farm Workers' Take Our Jobs campaign. Colbert is airing the experience this week on his Comedy Central show “The Colbert Report.” “It’s surprising there is so much hubbub over this,” said an aide to a Democratic member of the committee, who asked to speak on background. “Please, like Republicans haven’t called celebrities as witnesses before… At least Colbert worked for a farm for a day.” Some 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. Chaffetz, who has appeared on Colbert's show, said 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. 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.