Regional Express has rejected allegations of unsafe practices as "baseless", "cowardly" and "malicious".
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The regional airline has been the subject of media reports suggesting an employee's concern for the safety of an aircraft was repeatedly ignored.
Allegations claim the engineer was victimised by Rex after reporting a problem with a propeller.
The same propeller safety issue was claimed to have contributed to an incident over Sydney in 2017.
The accusations had been made against Rex after a 17-page report was leaked to the press.
The Australian Government's Civil Aviation Safety Authority have accused the Australian Licensed Aircraft Engineers Association of leaking the report.
A spokesperson for the trade union denied these claims on Monday.
Rex released a statement which claimed CASA was behind the leak.
Rex called the "baseless accusations" in the report the work of a "disgruntled engineer and his union".
Rex's chief operating officer Neville Howell said CASA was to blame for the bad press, not the airline's safety record.
"Some are now taking the despicable and cowardly approach of launching anonymous malicious attacks on Rex in the press," he said.
Mr Howard said Rex believed its safety culture was second to none.
A CASA spokesman said it had received information from the union that covered a "range of areas" and the matters raised had since been put to REX for comment.
"We are now reviewing all the information and responses carefully to determine what actions, if any, may be required," he said.
"If CASA has evidence of any safety issues we will take the appropriate action."
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