"Lion Man" Craig Busch smoked marijuana while handling lions at the Zion Wildlife Gardens where a handler was yesterday killed by a tiger, a park employee says.
Mr Busch is "categorically denying" the claim.
The park in Whangarei remains closed until further notice while investigations into the death of South African animal keeper Dalu Mncube continue.
Carpenter John Davis, who worked at the park for six years, told the Employment Relations Authority in Whangarei yesterday he would resign if Mr Busch was reinstated.
Mr Busch appealed to the authority to get his job back after he was sacked from the park run by his mother Patricia Busch late last year.
Mr Davis told the hearing Mr Busch had been sitting down with the lions when he last saw him smoking marijuana, the Northern Advocate reported.
He had not complained about the serious health and safety issue, because Mr Busch "was the management".
The park ran smoother after Mr Busch was dismissed, Mr Davis said.
A spokesman for Mr Busch said the Lion Man "categorically denied" using cannabis while handling lions and had given evidence to this effect during the hearing.
Mr Busch said the mauling was "a terrible personal blow".
Animal welfare and safety standards had slipped at the park since the breakdown of his relationship with his mother, he said during the employment hearing.
Mr Mncube, the park's most experienced big-cat keeper, was killed yesterday, when a tiger tore into his abdomen and lower leg, while two keepers were cleaning the tiger enclosure.
A message on the park's website says staff are focusing on supporting his family and would be organising counselling for all employees.
"We ask for your consideration at this difficult time and request you to please respect the privacy of those involved.
"This dreadful event is being investigated by the authorities and we will be cooperating fully with the investigations.
"Due to the investigations we are unable to comment further and the park will be closed until further notice."
Department of Labour spokesman Eric Janse van Rensburg said the park had not been closed down.
"The department has the ability to stop unsafe work practices or machinery where there is imminent danger of serious harm," he told NZPA.
He refused to comment further about the department's involvement while the investigation continued.
Northland police spokeswoman Sarah Kennett said that despite the best efforts of the other keeper, the tiger would not let go, and Mr Mncube died at the scene before an ambulance arrived.
Staff shot the tiger, Abu, to recover Mr Mncube's body.
Eight foreign tourists on a tour of the park witnessed the attack.
Mr Mncube had rescued a colleague from the jaws of the same 260kg tiger in February.
In that attack, he plunged his fingers into the gap between the tiger's 7.5cm-long teeth, before using a fire extinguisher to force the animal to release his Australian colleague, Demetri Price.
Mr Mncube said at the time of the February attack, it was over before he knew it, though Mr Price suffered four bites.
Mr Mncube's friend and colleague, Glen Holland, described him as "larger than life".
"People enjoyed being with him, people enjoyed being around him, he had an incredible ability with the cats."
Mr Mncube was the "best that we've seen at the park", Mr Holland said.
"Dalu was really the heartbeat of the whole lot - keeping everybody together."
NZPA