Planking was a shortlived craze in which people were photographed lying stiffly in unusual places.
Two employees were photographed by Mr Harris planking on objects between 1.5m-2.5m off the ground.
They received final written warnings and demoted to the lowest level roles in the plant's hierarchy.
Mr Harris, who had worked for Fonterra for 18 years, said he found the differences in discipline "very unfair".
But ERA member Helen Doyle said there was adequate explanation in the difference of treatment because of Mr Harris's senior role.
During disciplinary procedures Mr Harris made it clear that if he kept his job he would stand up and talk to people about health and safety.
He said it was one mistake in his 18 years of employment and sincerely wanted to go back to Fonterra.
However, Ms Doyle ruled in Fonterra's favour and said Mr Harris' dismissal was justified because the event and subsequent investigations disclosed serious misconduct.
Since losing his job, Mr Harris applied for 25 jobs and was eventually employed by another company in a lower paid role.
A Fonterra spokesman said today that the company had no comment to make on the ruling.
Mr Harris could not be immediately reached for contact.
Planking earned a poor reputation because of the dangerous places people did it. Australian man Acton Beale, 20, died when he fell from a seventh floor balcony while planking in Brisbane.