In a somewhat surprising move, the Eurosceptic 5 Star Movement could leave Parliament's EFDD group and join ALDE.
The Italian party counts 17 MEPs and could become ALDE's largest member.
Back in 2014, following the elections to the European Parliament, Liberal group leader Guy Verhofstadt said the 5 Star Movement was "incompatible" with ALDE's "pro-European political programme" and that allowing them to join the group "would be to abandon the European project and the urgent reforms it desperately needs. It is impossible for any responsible, pro-European group to take MS5 on board."
5 Star members have until noon today to vote in a referendum, and senior ALDE members will meet later today.
5 Star co-founder Beppe Grillo explained that staying in the Ukip-dominated EFDD group "is tantamount to facing the next two and a half years without a common political goal, in a delegation that has no interest in bringing home concrete results."
He also revealed that he had approached the Greens, but that the group had rejected his offer to merge.
In a blog post, Sylvie Goulard, a Liberal deputy who briefly sought the Parliament presidency, outlined a number of political and ideological differences between ALDE and 5 Star. She said, "Cooperation in the same parliamentary group could only lead to disavowals or contortions. Personally, I, like a certain number of my ALDE colleagues, am not prepared to do this."
Meanwhile, Patrizia Toia, head of the Italian delegation in the Socialist group, commented, " The manoeuvre currently ongoing between the 5 Star Movement and ALDE to build an alliance in the European Parliament is not an edifying sight. Beppe Grillo, after forging an alliance with Nigel Farage, now wants to move from the Eurosceptics to the Federalists, forcing voters to the humiliating ritual of a fake online election that only serves to affirm the arbitrary choices of their 'leader'.
“For his part, Guy Verhofstadt, running for President of the European Parliament, negotiator for Brexit and enemy number one of the Eurosceptic Farage, now does not exclude an alliance with the 5 Star Movement, which was rejected on the grounds of decency from political groups such as the Greens. This sort of incoherent backroom deal is exactly what alienates citizens from the European project."