Five months before the incident, an employee was punched in the head after a drinking session involving alcohol on site.
As a result, Auckland manager Ronald Neil put up signs in the canteen and around the offices telling staff liquor was banned from the premises.
He also sent a text message to all employees stating the ban was in place and told health and safety representatives, including the two men, at a meeting five days later.
On February 3, Mr Neil heard from another employee she had seen a group of workers drinking in the locker room the night before.
When he checked the rubbish bins he discovered "a number of empty beer boxes and bottles", and along with another manager, Baz Pritchard, decided to carry out an investigation.
It came to light a group of workers, including Nee Nee and Nathan, were drinking alcohol in the room after fishing together.
Nathan said on the afternoon of February 2, a group of men were drinking in the room and were "well on the way" and "happy" so he told them to go outside the liquor ban area, the ERA finding said.
Nathan denied drinking on the premises and Nee Nee said he had drunk only ginger beer.
However, the investigation concluded Nee Nee had invited a group of six employees to drink beer in the locker room and all five drank 66 bottles of beer between them.
In disciplinary meetings, Nee Nee and Nathan admitted they had initially falsely denied their involvement, saying they had acted unwisely.
In April they were dismissed for serious misconduct - a decision they appealed against.
ERA member Eleanor Robinson found that unlike the other men involved in the incident, Nee Nee and Nathan "had tried to mislead C3 about what had occurred ... and had not admitted their culpability until the disciplinary meetings on 5 April 2012".
Both were senior employees, union delegates, health and safety representatives and were aware of the liquor ban, she said.
The company had grounds to have lost trust and confidence in them and were not discriminated against, said Ms Robinson who found the company justified in dismissing them.