The Brazilian club have lodged a legal complaint in an attempt to see the agreement that Barcelona had with the forward's father's company regarding his transfer to Camp NouSantos have stepped up their fight to find out the exact details of Neymar's agreement with Barcelona by filing for an injunction.
The Brazil international joined Barca in early June last year for an estimated €57.1 million (£47.3m), although details released by the Catalans in January revealed that the total pre-wage expense was €86.2m (£71.5m).
The €57.1m included €40m (£33.2m) to Neymar's parents' company, N&N, owned by his father and mother, with confirmation of the deal in January causing Santos - who only received €17.1m (£14.2m) - to demand knowledge of the finer details of the 22-year-old's agreement with the Camp Nou club.
Neymar senior told Santos that he would explain the details of his 2011 agreement with Barca to them but refused to show them the documents, which infuriated the South American giants and they threatened to take legal action.
The Brazilian club have followed up on their warning and confirmed on Tuesday that they have filed for a legal injunction against N&N and Barca in a bid to see for themselves what the deal with their former player 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, February 10," the club said in a statement on their 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 [€40m] by the company mentioned above without the knowledge of Santos and the other economic rights holders of the athlete."
If their injunction is granted then Barca and Neymar Sr will be legally obliged to show Santos their agreement, unless a successful appeal is lodged.