Barcelona want to reclaim an €8.5m bonus paid to the Brazilian when he renewed his Barça deal past year.
Barcelona are to sue Paris Saint-Germain forward Neymar as he failed to honour the long-term contract that he signed a year ago.
The Brazil global completed his protracted transfer between the two clubs earlier this month when his £198m release clause was triggered.
Paris St Germain's record signing Neymar scored twice on his home debut as the 10-man side thrashed Toulouse 6-2 to go top of Ligue 1.
"Paris Saint-Germain reiterates that, like Neymar Jr, it has always respected all applicable laws and rules in its dealings and, once again, regrets the attitude of FC Barcelona". The club also claims that the Paris Saint-Germain subsidiarily assumes payment of these amounts in case the player cannot take over.
"There were three conditions [to the bonus]: one, that the player does not negotiate with another club in the last three months before July 31", Barca said at the time.
The Catalans are seeking to receive "8.5m euros (£7.8m) in damages, and an additional 10% in interest".
Barcelona has passed the complaint to the Spanish football federation (RFEF) after first filing the lawsuit in court, as well as demanding PSG subsidise it, should Neymar not be able to take responsibility for it.
"FC Barcelona has started these proceedings to protect its interests following Neymar's decision to buy out his contract just months after he signed an extension until 2021". But with them [the board], no. I spent four attractive years there and I parted happy.
"I hope things get better for Barca and that they go back to being a team that can compete".
On Monday Neymar said Barcelona deserved "much more" than the current board of directors and added that it made him "very sad".