Audit documents submitted by prosecutors to Spain's National Court detailed a total of €15.2 million ($19.2 million) of spending by former managers, including €54,800 by Rato.
The 86 suspected users of the credit cards also included Rafael Spottorno, who was manager of Spain's royal household under the former King Juan Carlos.
The heads of several senior officials rolled on Thursday and Friday.
These included Pablo Abejas, who was fired as third-in-command in the Madrid regional economy ministry and Jose Ricardo Martinez, who resigned as leader of the top UGT labour union in Madrid, sources in their offices told AFP.
Among other names in the court documents were members of political parties including the opposition Socialists (PSOE).
The Socialists' new leader Pedro Sanchez said on Twitter on Friday: "I am ashamed that PSOE activists are involved in the credit card affair. I apologise for it."
The party said it would investigate which members were involved and expel them from the PSOE.
The Bankia documents, seen by AFP, were submitted by prosecutors to the court for its investigation into the privatisation of the banking group.
The near collapse of Bankia in 2012 caused thousands of customers to lose their savings and pushed Spain to seek an international bailout for its financial sector.
The documents, which contain findings of an internal audit of the company, indicate spending on non-work-related hotels, restaurants and trips by former directors of Caja Madrid, one of the regional banks that make up the Bankia group.
Former economy minister Rato is one of the best-known financial figures in Spain and a prominent figure in the ruling conservative Popular Party.
He served as managing director of the International Monetary Fund from 2004 to 2007.
He was chief executive of Caja Madrid and held the top post at Bankia from 2010 to 2012.
Rato has made no public reaction to the latest allegations.
Anti-corruption prosecutors said in a statement that the credit cards were given to the managers "outside the established sphere" of professional expenses.