While O'Brien's restraint of trade period was for three months, the ERA member considering her case said it was appropriate to exercise their "discretion" and modify the duration of the three-month non-compete restraint by five weeks to seven.
"For the sake of clarity the final day of the modified non-compete restraint is March 14, 2022," the ERA said.
The ERA said evidence established that in her role with MediaWorks radio as the host of the new Today FM show, O'Brien "will be working in competition with Discovery".
"Given the restraints as modified are reasonable and enforceable if Ms O'Brien commenced work with [MediaWorks Radio] on January 25, 2022, she will be in breach," the ERA said.
"Standing back, looking at that figure, including in comparison to other cases, I conclude that a fair penalty is $2,000. Ms O'Brien is ordered to pay a penalty to Discovery of $2,000 to compensate it for the inconvenience and resources expended in pursuing this matter. The penalty is to be paid within 21 days of the date of this determination," the authority said.
MediaWorks Director of News and Talk Dallas Gurney said plans are underway to launch Today FM in the first quarter.
"We have backed Tova 100 per cent throughout the process and can't wait to have her join us at Today FM," Gurney said.
"We look forward to announcing the launch date for our new station soon and getting the Tova breakfast show underway when she is permitted to join MediaWorks."
The determination found O'Brien had been involved in MediaWorks' business before her employment with Discovery ended.
"She approved a quote for inclusion in a press release announcing her appointment... along with the launch of a new talk radio brand and allowed her image to be videoed for the purposes of a promotional video for that new brand," it said.
"I am satisfied there was a prima facie conflict of interest in her involvement in both activities."
The $2,000 penalty which O'Brien has been ordered to pay was to compensate Discovery "for the inconvenience and resources expended in pursuing this matter".
It was revealed last week that O'Brien's transition to her new role at Mediaworks had hit a legal snag.
The journalist, who had been with Newshub for 14 years, argued to the ERA that her soon-to-be role as a breakfast radio host is not similar to her role as political editor on TV3.
She took the dispute to the ERA after mediation failed. A three-day hearing in Auckland finished on Thursday.
O'Brien presented her final bulletin as Newshub's political editor on Friday.
In an emotional post shared to Instagram, O'Brien wrote, "Lots of tears today, happy and sad, as I sign off for the last time.
"It's the people that make the place. Thank you to my 3News/Newshub whānau for making the last 14 years the best 14 years."
Owner of Newshub, Discovery, said it is "archaic" to think that radio and television breakfast news shows are not in direct competition with one another.
Discovery argued that Newshub's The AM Show will compete for the same audiences and advertising dollars as O'Brien's new radio show with MediaWorks.
MediaWorks previously owned TV3 but sold its TV arm to Discovery in September 2020. Now O'Brien is jumping back to MediaWorks.
The launch date for her Today FM hasn't been confirmed but is rumoured to be this month. If so, it would coincide with the return of TV3's new AM Show, expected back on air next month.
O'Brien announced her resignation at the beginning of November last year in time to finish at Discovery before Christmas, take a month's leave, and finish out her contract in time for Today FM's launch by the end of this month. But then Discovery told her it would be enforcing the three-month restraint clause in her contract.
The hearing came after the failure of mediation between the parties.
