While MUNZ acknowledged genuine Covid risk at the border, it argued that risk did not arise from union officials visiting a site but from seafarers on board vessels who travelled internationally.
ISO said it was not imposing new health and safety policies on MUNZ for the purpose of preventing access but rather required compliance with existing procedures and Covid-10 operational control measures.
ERA member Nicola Craig said there was an absence of any expert medical or other opinion to justify ISO's position that a serious risk needed to be managed and limitations on access to the port was an appropriate vehicle for doing so.
"Even if the company was able to establish a procedure was in place which prevented access to the port altogether, I have serious reservations about whether that would be reasonable," she said.
At the investigation meeting, Craig said ISO had difficulty establishing what its own control measures were and described them as being under constant review and may be updated as new information or guidance came to light.
The company's representative accepted in closing submissions the evidence on what the current protocols were was unclear, she said.
Harrison said ERA has sent a strong message to employers who tried to undermine the right of workers to meet with union reps on the job.
He said the determination was crystal clear there had been an ongoing breach of the employer's obligations to allow access.
ISO did not respond to a request for comment, including whether it will appeal the ERA's determination.