Stewart, a Republican, is the founder of The Shipley Group, a Farmington-based consulting firm that specializes in environmental and engineering issues.
But Stewart had been criticized for touting a "government is the problem, not the solution" message while his firm lists several clients from the federal government - including the U.S. Environmental Protection Agency, the U.S. Department of Agriculture and the U.S. Air Force.
Alan Seim, campaign manager for Stewart's opponent, Jay Seegmiller, said that was hypocritical.
"We see that hypocrisy in him taking federal money," Seim said. "We're concerned his actions don't match his words."
U.S. Chamber of Commerce President and Chief Executive Officer Thomas Donohue wrote a letter supporting Stewart, saying his "election to the U.S. House of Representatives will help produce sustained economic growth, help create more jobs and get our country back on track."
The two candidates recently squared off in a debate and are scheduled to have two more before the election - including one on Oct. 10.