By Jack Fink, CBS 11 News

DALLAS (CBSDFW.COM) – The largest taxicab company in North Texas is facing some serious allegations.  Former employees accuse the company of cheating them out of thousands of dollars — and even covering up Medicaid fraud.

For five years, Patsy Warren of Fort Worth says she put up with working 12 hour days — and driving hundreds of miles each day.   Warren says, “I needed the money. I needed the job.”

Warren says she drove a marked yellow cab for Irving Holdings, which owns the taxi company.

Irving Holdings has the state’s $20 Million contract to take patients enrolled in the Medicaid program to and from their doctor’s appointments.  Yet despite Warren’s long trips and long days, Warren says, “lots of times, we weren’t even paid minimum wage.”

So Warren quit and filed a federal lawsuit against Irving Holdings.  Warren and other drivers accuse the company of violating federal labor laws, claiming they’re owed back wages, overtime, and other benefits.

Mike Jones is Patsy Warren’s son-in-law, and worked in the company’s accounting department for three years.  He says he always heard the Medicaid drivers complain.  “They would only get a partial check for what they should have earned, and never get the rest of it.”

Jones says he was hired to make sure drivers weren’t trying to cheat the system.  But the more he looked.  “The biggest surprise was the company was helping to cover-up the fraud.”

According to the company’s internal logs, management repeatedly fined drivers $500 for falsely claiming they made trips and billing Medicaid.  But in a deposition for the lawsuit, Jones says after fining drivers, the company kept the money for itself, and didn’t report the fraud to the state.

Jones also says in the deposition that when state auditors showed up at the office, he was forced to alter company documents that mentioned driver fraud.  “We’d do it behind the auditors’ backs while they were there.  Hide signatures. Cover-up signatures. Whiteout paperwork. Print new paperwork.  If we lost the contract, they’d lose millions of dollars.”

So what does Irving Holdings have to say? CEO Jeff Finkel says because of the on-going lawsuit, he wouldn’t comment.  In court papers though, the company denies any wrongdoing.

Dallas attorney Joel Fineberg represents Warren and other cab drivers.  He says, “In some cases when we looked at their checks they were only making about $35 a day.”

A judge has conditionally certified it as a class action, and about 200 other current and former drivers could join.

As for Patsy Warren, she has a message for the CEO:  “He needs to do right for the people who work for him.”

The trial is set to begin next October.  CBS 11 called the Texas Medicaid program to find out if the state is following up on these allegations of fraud.  A spokesperson told him the lawsuit won’t impact their contract with Irving Holdings.