SACRAMENTO -- A California company that supplied more than a third of the heavy firefighting air tankers grounded by the government said Monday it is unfairly being lumped in with a Wyoming firm responsible for most of the catastrophic accidents.

The U.S. Forest Service and Interior Department this month canceled all contracts for use of 33 air tankers that usually drop retardant on fires during the summer, citing safety concerns after two planes broke up in midair in 2002.

"We have been unjustifiably put in the same category as the company that is responsible for five of the six structural accidents that have occurred in the last 30 years," said Terry Unsworth, president and chief executive of Aero Union Corp. of Chico.

Both of the deadly 2002 accidents over California and Colorado involved aircraft operated by Hawkins & Powers Aviation Inc. of Greybull, Wyo. Both planes lost their wings in mid-flight while dropping fire retardant.

An Associated Press investigation found Hawkins & Powers had a long history of crashes and safety problems. By contrast, air tanker pilots, industry experts and a government inspector called Aero Union an example of a company that was able to maintain high standards while competing for government low bids.

Aero Union says it has been able to avoid problems by upgrading its planes and training its pilots. Court records show the company spent $3 million to modify each old military plane it obtained from the government.

Unsworth complained that his company wasn't consulted nor its operations inspected before the National Transportation Safety Board, Interior Department and Forest Service decided they can't guarantee that the old air tankers can be safety operated.

The company plans to fight the decision by seeking support of congressmen who are concerned about similar companies in other states, and who say grounding the heavy air tankers imperils firefighting efforts.

The government says it can function using helicopters, smaller planes and military aircraft, though the Interior and Agriculture departments now say they may reinstate some of the large tankers if the Federal Aviation Administration agrees to certify they are safe.

In the meantime, the grounding is having a "devastating effect" on Aero Union, which will lay off many of its employees, Unsworth said.

Hawkins & Powers referred calls for comment to a spokeswoman who was said to be unavailable, and who did not return a voice mail message.

Meanwhile, Monday marked the official start of fire season began for all of California south of Sacramento. Fire season in the rest of the state is expected to begin June 1.