Giannis Varoufakis and a German MEP are sueing the European Central Bank.
Their aim is to gain access to a document related to the ECB's decision to "freeze" funding to Greek banks in 2015, according to Reuters.
The former Finance Minister of Greece and German MEP Fabio de Massi are asking the European Court of Justice to force the ECB to disclose the legal opinion on which the decision was based, claiming it may be illegal.
"By limiting the liquidity of the Greek banking system, to press for pension cuts, tax increases and privatizations, the ECB exceeded its mandate," De Massi told Reuters.
After the ECB rejected their request, Mr Varoufakis and Fabio de Massi are turning to the Court of First Instance of the European Communities to obtain the document. An ECB spokesman told Reuters that the legal opinion was preceded the decision to "freeze" funding by two months. He added that the ECB has decided not to disclose it in order to protect its legal advisers and consultants.