Emery will reappear in court on April 30.
"Our parking officers are good men and women who are simply trying to do their job. Not one of our staff deserves to be treated like this, irrespective of what people think about the profession," Patena said.
"The officer wants me to convey their sincere gratitude to the members of the public who rendered assistance straight away and to the officer's colleagues who arrived at the scene in a matter of minutes."
The alleged assault follows other reported attacks on parking officers in recent years.
Incidents included an Auckland parking officer being beaten and left with a fractured rib and a partially collapsed lung and another warden in Timaru being shot with a BB gun.
Bill Newson, national secretary of union E tu, said he was not aware of the details of the latest assault.
"But we are generally concerned as a union for the health and safety of people like parking wardens and security guards who are often working in the public domain and caught in stressful situations," he said.
"And our concern is that they are trained and supported adequately to be able to cope with that."