Two Las Vegas Valley cab companies argued they had no knowledge of falsified smog tests in a Nevada Department of Motor Vehicles appeal hearing Wednesday.

Attorneys representing Nellis Cab Co. and Desert Cab Co. claim that the companies didn't know that their state-licensed inspector wasn't properly testing the vehicles, and the cab firms shouldn't be punished financially as a result.

"There never was any conspiracy for this to happen," attorney Bob Winner said.

DMV investigators argued that knowledge of the improper testing doesn't make a difference under state law.

In July, the DMV accused Nellis, Desert and four other cab companies of using fake emission inspection reports to certify 118 taxis which hadn't been smog tested, as required by law.

The state alleged the faked tests involved "cold piping," where one car is tested and its test results are applied to another cab.

The DMV required the companies to retest and reregister all of the vehicles in question.

Four companies -- Nevada Yellow Cab Co., Nevada Checker Cab Co. and Nevada Star Cab Co., which are all owned by the same company, and Western Cab Co. -- all decided to cooperate with officials and not appeal the decision. Nellis and Desert decided to appeal the decision, and also retest the 71 cabs in question.

DMV investigators are still looking into whether criminal charges will be filed against any of the cab companies, and have not publicly named four emissions inspectors implicated in the matter.

Administrative Law Judge Kathleen Hicks said a final decision on the appeal might take more than 30 days.