MacMahon reported Cuban specifically discussed the proposal to allow coaches to challenge certain calls, which was eventually unanimously approved on a one-year trial for the the 2019-20 season.
When reached for comment about the fine by MacMahon, Cuban took the situation in stride. "I appreciate the irony of your reporting on a fine that someone should, but won't, get fined for leaking to you," he said.
This isn't the first time the league levied a fine against Cuban, and it's far from the biggest financial hit he has received.
The NBA handed down a $500,000 penalty in January 2002 after Cuban was critical of the league's officiating on multiple occasions. He had to pay $600,000 in February 2018 after admitting he had spoken to Mavericks players about the team's plans to tank for the remainder of the 2017-18 season.
Regarding his most recent infraction, MacMahon noted anybody attending a Board of Governors meeting is prohibited from speaking about what happened behind closed doors.