European lawmakers on Tuesday complained that a visit by eco-warrior Greta Thunberg to European Parliament is set to go ahead despite a moratorium on all outside visits to the chamber.

In a letter to parliament president David Sassoli, conservative MEP Nuno Melo of Portugal asked what justified an "exception" when "in matters of health risk, human beings are democratically equal".

"How can we explain this to our visitors and guests", added Belgian MEP Hilde Vautmans, a liberal, in another letter to Sassoli.

"Everyone should be treated equally. If the European Parliament grants an exception to Greta Thunberg, this house will not be taken seriously," she added.

Sassoli on Monday announced the immediate suspension of all visits to the European Parliament, a measure that applied not only to tourists, but also to guests of MEPs, their assistants and lobbyists.

Swedish climate activist Greta Thunberg is to address the European parliament on Wednesday
Swedish climate activist Greta Thunberg is to address the European parliament on Wednesday AFP / GEOFF CADDICK

But Thunberg's speech to MEPs in Brussels on Wednesday is still set to go ahead.

"This is not a decision linked to a particular person," a spokeswoman for the institution told AFP.

"Any speaker specifically invited by the president of an official body of the parliament is allowed to attend" if he or she respects the health rules, the spokeswoman added.

On Twitter, French MEP Nathalie Colin-Oesterl? was surprised by the invitation to the 17-tear-old Swedish campaigner.

"My assistant is not allowed to come to the plenary session in Strasbourg (next week), but Greta Thunberg will be there tomorrow", she said.

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