Denver Yellow Cab, Metro Taxi, and Freedom Cab are accused of violating what is called the "80 in 8" rule.
The rule stipulates drivers are not supposed work for more than 80 hours in an eight-day period.
The Colorado Public Utilities Commission (PUC) investigated three companies at Denver International Airport in February 2009 and assessed fines against the companies.
Freedom Cab paid nearly $40,000 in penalties in December of last year after investigators found the company in violation of the 80 in 8 rule 29 times.
"We are trying to work on it and hopefully it won't happen to us any more," Freedom Cab Manager Max Sarr said.
Denver Yellow Cab was assessed a $165,000 penalty for 60 violations.
The company will only have to pay a $50,000 penalty, an administrative law judge ordered, and agree to quarterly safety reports over the next year and a half.
"When the drivers don't comply, it is Denver Yellow Cab's responsibility to stand up for that," Ric Fanyo, an attorney representing the company, said.
Fanyo says the violations involved three drivers, all three of whom no longer work for the company.
As for Metro Taxi, a different administrative law judge threw out a proposed plea deal, which will now have a hearing to determine how much it may have to pay for its 54 violations of the 80 in 8 rule.
Metro Taxi representatives did not return phone calls Tuesday.
Many drivers are working long hours, they say, because of their high lease fees for their vehicles per week.
"I'm paying $750 for four days out here," Yellow Cab driver Doug Place, who works at DIA four days a week, said. "What the PUC needs to do is look at what the companies are actually charging their drivers."
PUC spokesman Terry Bote did not address those concerns, but says the agency assessed fines against the companies because of the safety concerns for passengers.
"We want the drivers to be rested," Bote said. "We want the passengers to be safe and we want the companies to take responsibility for making sure their drivers are complying with the laws."
(KUSA-TV © 2010 Multimedia Holdings Corporation)