The employees of Illinois-based Prospect Airport Services say managers haven’t responded to their complaints.
Prospect is a DIA contractor and works with Frontier Airlines and Southwest Airlines.
The Service Employees International Union local unit helped organize Tuesday’s walkout.
Union spokesman David Fernandez says the workers, who aren’t union members, are asked to escort several wheelchair passengers at a time and carry heavy baggage without safety belts.
Workers say they also handle baggage containing firearms without training.
Telephone calls seeking comment from Prospect and Frontier weren’t immediately returned.