Cabs line up at McCarran International Airport on Thursday. Investigators think that emissions tests on 118 taxicabs in the valley were conducted by "cold piping," in which another vehicle is tested in place of the car of record. Photo by Jane Kalinowsky.

A half-dozen Las Vegas Valley taxicab companies are accused of using fake emissions inspection reports to certify 118 taxis that hadn't been smog tested, Nevada Department of Motor Vehicles officials said Thursday.

The companies were served with violation notices this week. Four emissions inspectors whom officials accused of being involved in the scam had their licenses revoked last month.

"We have not had a previous experience with companies doing fraudulent smog checks like this," said Kevin Malone, a DMV spokesman. "We've had plenty of cases of individual smog check inspectors (committing fraud), but nothing on the part of cab or limo companies."

Investigators believe the emissions tests were conducted by "cold piping," in which another vehicle is tested in place of the car of record.

"They typed in information for one car, and they plugged another car into the machine," Malone said. "It almost has to be that someone at the cab companies had knowledge of it."

Citing an ongoing investigation, Malone would not say whether bribes were offered in return for the emissions tests, which he said took place between last July and January.

"We don't think there are other cab companies" involved beyond the six cited this week, Malone said. "We are looking into other smog-check operators."

Among the companies cited is Nellis Cab Co., with 45 cited cabs, DMV officials said. That is nearly one-third of the 130 full-time cabs the company is licensed to operate.

Other cited companies were Western Cab, with 34 implicated cabs among 130 full-time taxicab licenses; Desert Cab, with 26 cited cabs out of 136 full-time taxicab licenses; Nevada Yellow Cab, with seven cited cabs among its 201 full-time taxicab licenses; Nevada Star Cab, with four cited cabs out of 201 full-time taxicab licenses; and Nevada Checker Cab, with two cited cabs out of 129 full-time taxicab licenses.

Bill Shranko, operations director at Yellow Checker Star Transportation -- the valley's largest cab operator and owner of Yellow, Checker and Star -- denied any intentional improprieties on his company's part.

"There was no fraudulent intent at any time from our company," he said. "Right now, we're checking and investigating" internally.

However, Shranko conceded that he could not rule out some sort of error or fraud perpetrated by individual employees or contractors.

"I hope that's not the case," he said. "No matter what it is, we'll cooperate like we always do with the DMV in their ongoing investigation."

Messages left at Nellis and Desert were not immediately returned. Attempts to contact officials at Western were unsuccessful.

The citations follow a nine-month investigation in which inspectors used driving logs and other documents to confirm that cabs were on the streets at the times of the tests.

Malone did not know if the cabs in question were incapable of passing smog checks, or if the testing was done simply to expedite the process. He also declined to name the four cited inspectors or the company or companies for whom they worked.

The taxi companies have until July 14 to request a hearing or turn in vehicle registrations for the cabs in question. Shranko said his company would ask for a hearing, which is tentatively set for Aug. 1-4.

If the companies are found guilty, registrations for each of the cabs in question will be canceled, and those cabs will have to be tested and reregistered.

The DMV does not have the authority to fine the cab companies but can ask for criminal prosecution on some sort of gross misdemeanor charges if desired. That did not appear likely.

This is the second time the cab industry has been slapped by regulators this year.

In April, 13 of the valley's 16 cab companies were cited by the Nevada Taxicab Authority after cabs that were restricted to pickups at the Las Vegas Convention Center allegedly went trolling for fares elsewhere.

The latest charges come at a sensitive time for Nellis and Desert, whose owners and managers are asking the Taxicab Authority to allow them to form a 17th cab company in the valley.