Mr. Juncker was visibly shaking with indignation.
"The European Parliament is ridiculous, very ridiculous. The fact that about 30 MEPs are seated in this debate is enough to show that the Parliament is not serious," he said on Tuesday (July 4).
Mr. Juncker petulantly said he would never attend "a meeting of this kind" again.
Speaking in French, but switching occasionally to English, he suggested the Parliament "would have a full house" if Angela Merkel or Emmanuel Macron had been present, rather than Malta's Joseph Muscat, the Maltese prime minister, who recently handed over the EU presidency to Estonia.
Mr. Tajani, switching easily between Italian and French, reacted angrily to Mr. Juncker's criticism.
He urged Mr. Juncker, a former prime minister of Luxembourg, to show "respectful behavior" and "use different language," and said he had no right to "control the Parliament."
"We are not ridiculous. I beg of you," added Mr. Tajani.
The European People's Party (EPP), which represents mainly center-right parties, said they were going to hold an internal debate on Wednesday (July 5) about the issue of absenteeism.
That followed a low turnout at a plenary on June 14, when Hilda Heine, president of the Marshall Islands, was greeted by a virtually empty chamber.
"She had spent maybe 18 hours on the plane and very few people showed up in plenary," the official said.
Doru Frantescu, director of VoteWatch Europe, said it was "uncommon" for so few MEPs to turn up to a plenary session being addressed by the European Commissioner.
"We are still trying to figure out exactly what happened. Usually there are many more, but the variations in number depend on how interesting the debates are," he told Sputnik.
"Sometimes there are only 20 MEPs there, at other times it could be hundreds. It depends on the subject. For example, if it is about fisheries you won't get anyone from Austria there," he said.
"There are records of attendance for MEPs but they are per day, not per hour. They are not tracked every hour they are in the European Parliament building. They could be in their offices, in meetings or committees. Just because they are not in the chamber, it does not mean they are not working," Mr. Frantescu told Sputnik.
Thanks to the EU Maltese Presidency for making progress on key priorities that concern European citizens. pic.twitter.com/6nyjEGgEaH— EP President Tajani (@EP_President) 4 July 2017
He said British MEPs have the worst attendance record in Europe, while two MEPs have attendance records of 99.6 percent, Italy's Nicola Caputo and France's Francoise Grossetete.
Mr. Frantescu said it was "understandable" that the EPP would have an internal debate about absenteeism, because Mr. Juncker was a leading light in the EPP.
"They are trying to get to the bottom of what happened because they no doubt feel uncomfortable that they have embarrassed him," he told Sputnik.
Last month an investigation by a group of 48 journalists, found that although each MEP gets 4,295 euros (US$4,875) every month, mainly to fund an office in their own country, the offices for 249 MEPs do not exist or "seem nowhere to be found."
It was reported in April that MEPs were spending up to US$43.5 million per year in expenses, without any checks on their expenditure.