LUXEMBOURG — If EU lawmakers were forced to declare how they spend their monthly expenses, they would be criticized so much that they could struggle to do their job, a lawyer representing the European Parliament said Thursday.

She was speaking during a three-hour public hearing at the European Court of Justice on parliamentary expenses. A group of journalists brought a case to court after the Parliament refused to give them access to information on how MEPs spend public money. Last year, around €450 million was spent on MEPs' salaries, travel expenses and office costs.

"If everything was visible ... it would impose a big pressure on [MEPs]," said the lawyer representing the Parliament, later suggesting that "if everything was under discussion by journalists ... in a time where everything is discussed on Twitter," MEPs would in effect be censored and unable to exercise their "free mandate."

It was "completely untrue" to suggest MEPs' activities weren't already visible enough for the public to hold them accountable, the lawyer argued. She said the Parliament's website allowed people to see what their representatives are doing in committees, saying this was evidence the institution was "extremely transparent."

"MEPs need to be given a space to think," she added.

The Parliament said that giving access to the information would violate MEPs' privacy.

The Parliament dismissed the journalists' request for information in 2015 in part because it would be "an excessive burden" to provide them with the documents in question. The institution's lawyer confirmed during the hearing that the documents numbered in the millions and were in paper format — which was described by one judge as "quite astonishing."

"The filing system is what it is," said the lawyer.

She said the Parliament estimated it had almost 900,000 individual pieces of paper for MEPs' travel expenses between 2011 and 2015 — kept in 48 cupboards filled "from ceiling to floor." This, the lawyer said, was only the tip of the document iceberg.

Speaking to POLITICO after the hearing, Anuška Delić, a journalist who brought the case, said: "I can’t get over the shock of hearing this."

However, she pointed out that a global consortium of journalists, to which she belongs, had managed to sift through 11 million documents leaked from the law firm Mossack Fonseca — resulting in what became known as the Panama Papers scandal.

The Parliament also said in some cases they simply didn't have the documents in question, in particular for the so-called General Expenditure Allowance [GEA] worth around €4,300 a month, which is usually paid directly into an MEP's bank account.

"Whether this is correct or not correct, whether or not the GEA should be paid in a lump sum ... we do not hold the documents," said the lawyer. The Parliament said it had internal controls in place to allow funds that were incorrectly spent to be recovered.

The Parliament also said that giving access to the information would violate MEPs' privacy, a suggestion that Delić's lawyers rejected during the hearing.

"We are not demanding data that covers the private lives of MEPs but strictly their professional duties," said Delić.

The Court did not give a date when it will rule in the case.