When it comes to the right of public access to EU documents, it is the content of the document that matters and not the device or form. If text messages concern EU policies and decisions, they should be treated as EU documents,” Ms O’Reilly said.

The ruling has prompted heavy criticism of Ms von der Leyen, including calls for her resignation, from MEPs.

Transparency ‘cornerstone of democracy’

Sophie in ‘t Veld, a Dutch MEP, accused the Commission of becoming less transparent under Ms von der Leyen’s leadership.

She said: “This is bigger than just text messaging between von der Leyen and Pfizer.

“In a democracy, transparency is the cornerstone of any relationship between an executive and the legislature that checks the executive’s power.

“The European Commission has become less transparent, less accountable to the European parliament and frankly more unhinged from European democracy.”

Difference between ‘democracy and tyranny’

Cristian Terhes, a Romanian MEP, said she should resign. He said: “Transparency, along with the respect for individual fundamental rights, is what makes the difference between democracy and tyranny.

“The behaviour of Ursula von der Leyen, in failing to disclose text communications over contract negotiations she had personally with Pfizer’s CEO on behalf of the EU, was anti-democratic, anti-European values, and proves a resolute lack of transparency. This is tyrannical behaviour and she must resign immediately.”

Ms von der Leyen has a history of controversy over text messages. As German defence minister, she was slammed for deleting mobile phone communications amid an investigation into procurement contracts she was overseeing.