Maestri fined over referee rant
This followed his side's controversial Six Nations win over Wales earlier this month.
A Six Nations disciplinary committee suspended half the fine, with the lock not having to pay the outstanding amount provided he avoids further sanction between now and the end of the 2017/18 season.
France ended their Six Nations campaign on March 18 with a 20-18 victory at the Stade de France that saw Barnes allow an extraordinary 20 minutes of added-on time, with the home side camped on the Welsh line as they sought a clinching score.
Following a match full of disputed incidents, Toulouse forward Maestri was quoted as saying: "Anglo-Saxon referees always talk about fair play but the reality is that they think we [the French] are cheats."
That prompted officials to bring a misconduct complaint against the second row.
At a disciplinary hearing in London on Wednesday, Maestri accepted he had "committed an act of misconduct and openly apologised for making the comments", according to a Six Nations statement.
Maestri has the right of appeal.
The Six Nations have yet to make a decision on arguably the most contentious incident of the match – the dispute over whether France prop Uini Atonio suffered a genuine head injury that meant he had to be replaced.
With France 13-18 behind and camped on the Welsh line, a series of scrums took place late in the match as they went in search of an equalising try.
In the midst of all this, Atonio was replaced – despite telling Barnes he was not injured but his back was hurting – by preferred tighthead prop Rabah Slimani, known for his devastating scrummaging power.
France coach Guy Noves insisted it was a genuine call by his medics for a head injury, which would leave Barnes with no choice but to allow France to bring back the previously substituted Slimani under rules governing the treatment of suspected concussion.
But Wales caretaker coach Rob Howley said there was "evidence to suggest that the integrity of the game has been brought into disrepute" by France fabricating the head injury call.
France eventually got the try they wanted in the 100th minute, with the ensuing successful conversion securing a win that saw them finish third in the Six Nations, with Wales fifth.
Officials have already decided they will take no further against France wing Virimi Vakatawa, who received a yellow card for a high tackle.
They also said no action would be taken following an allegation from Wales's George North he had been bitten as they had been unable to conclude any individual player had committed foul play against the wing.