British conservative Daniel Dalton, Belgian Vice-Chair of the Committee on Economic and Monetary Affairs, Sander Loones, and Ramon Termosa, of the Spanish Convergencia party, have raised concerns that Spanish banks bailed out by European taxpayers provided guarantees for the transfer fee.
A leaked report from whistleblowing website Football Leaks revealed last month that Bale cost in excess of €100 million ($109 million, £77 million) despite Madrid previously insisting the deal was worth €91 million.
"Promissory notes were issued to Tottenham Hotspur, which subsequently seem to have been sold on to Spanish banks, which have now ended up assuming the risk for Bale's record-breaking transfer fee," read the question form signed by all three MEPs on Wednesday.
"Is it correct to state that bailed-out Spanish banks were offering promissory notes to Tottenham to act as a guarantee, thereby indirectly putting the liability on the Spanish and European taxpayers?"
In 2013 Dutch MEP Derk Jan Eppink claimed one of the banks involved in the agreement was Bankia, which had been bailed out to the tune of €18 billion by the European Stability Mechanism.
"This would indirectly transfer the cost of the transfer to European taxpayers constituting illegal state aid," Tremosa added in a statement.
"Real Madrid are the world's richest football club and if it has used a state owned bank, owned by taxpayers to guarantee multi-million pound record transfer fees, then it is clearly something the EU should look to address to ensure there are no unfair competitive advantages given to football teams supported by taxpayer-funded financial institutions," Dalton told the Daily Telegraph.