The Brazilian club has lodged a legal complaint in an attempt to see the transfer agreement that Barcelona had with Neymar's father's company.
The Brazil international joined Barca in early June last year for an estimated 57.1 million euros, although details released by the Catalans in January revealed that the total pre-wage expense was 86.2 million euros.
The 57.1 million euros included 40 million euros to Neymar's parents' company, N&N, owned by his father and mother, with confirmation of the deal last month causing Santos — which only received 17.1 million euros — to demand knowledge of the finer details of the 22-year-old's agreement with the Camp Nou club.
Neymar's father told Santos he would explain the details of his 2011 agreement with Barca but refused to show the documents, which infuriated the South American giants.
The Brazilian club has followed up on its warning and confirmed Tuesday that it has filed for a legal injunction against N&N and Barca in a bid to see for itself what the deal was.
"After exhausting all attempts at amicably obtaining the contracts and documents signed between N&N or Neymar to Barcelona, Santos handed an injunction against these companies in late Monday 10 February," the club said in a statement on its website.
"The injunction by Santos seeks to obtain such documents to allow them to be analysed, so that the club know the reasons for the receipt of [40 million euros] by the company mentioned above without the knowledge of Santos FC and the other economic rights holders of the athlete."
If the injunction is granted, Barca and Neymar's father will be legally obliged to show Santos the agreement unless a successful appeal is lodged.