S&D group leader Gianni Pittella has called for further studies before any final decision is taken on the future of Parliament's building in Brussels.
The Italian deputy was responding to news that the bureau of the Parliament is reportedly considering spending almost half a billion euros to rebuild part of its building in the city.
Parliament's administration, under Secretary-General Klaus Welle, is considering options that include refurbishing the building or a total rebuild.
The bureau, comprising Parliament's President Antonio Tajani and 14 vice presidents from the ranks of the 751 MEPs, met in Strasbourg on Monday to discuss the renovation of the Paul-Henri Spaak (PHS) building.
The PHS building includes the hemicycle where plenaries take place when Parliament is in session in Brussels, as well as Tajani's office and facilities for receiving visiting VIPs. The building was completed in 1993 at a cost of 42bn Belgian francs, or just over €1bn.
Monday's meeting was accompanied by a presentation of the technical evaluations by the French Building Science and Engineering Centre (CSTB).
Speaking at a news conference in Strasbourg on Tuesday, Pittella said, "I recommended and request further studies on this matter because the current studies come to different conclusions.
"One consideration is safety. But, for sure, if are obliged to spend so high a figure the cost needs to be fully justified and we need to know why we are spending this sort of money.
"I am not in favour of acting right away, not until there have been further studies. We could then make a decision as a whole Parliament."
Further response to the news about the "unsafe" building came from Ukip budget control committee member Jonathan Arnott.
He said, "How about we tear the whole thing down and don't bother rebuilding at all. EU institutions rob the nations within it of making their own laws, deciding their immigration policies and making their own global trade deals.
"They are democratically dangerous as well as ridiculously expensive. Why should ordinary taxpayers have to pay for MEPs to live in such salubrious surroundings?"
He added, "The collapsing roof of the parliamentary hemicycle is a metaphor for its lack of democratic support, as participation in European Parliament elections is at a multi-decade low with less than half of the European peoples even bothering to vote.
"If the EU believed in democracy it would ask the peoples of Europe by referendum if they wished to pay the half a billion euro for a new building as well as spend €200m a year for the Parliament's travelling circus to Strasbourg. The EU knows this proposal would be flatly rejected by the peoples and so never consults with those who pay the bills."
On Tuesday, Parliament issued a statement which read, "On the basis of the discussion held and the technical analyses, the bureau has charged the Secretary-General to present, at a later stage, detailed proposals on possible solutions for the refurbishment of the Spaak building."
It went on, "The proposals should address all potential options under discussion. These include no action, renovation and reconstruction. The proposals should be accompanied by detailed assessments on the feasibility of the projects, in particular as regards to the duration and cost, and address any relevant legal matters, especially with regard to liability issues.
"Until the finalisation of the studies and consequent decision, the bureau has charged the Secretary General to continue to implement and take all necessary measures to ensure the safety and security of the building and the staff."