The leader of the Socialists & Democrats group, the legislature's second largest, said he had recommended to Adrian Severin that he quit parliament as well but Severin had refused.
Severin, a former foreign minister, is the third member of the European Parliament to come under fire after journalists from Britain's Sunday Times newspaper posed as lobbyists and enticed them to agree to amend laws in return for money.
Severin is shown on a video posted on the Internet outlining how he put forward amendments to laws at their request, agreeing to send an invoice.
But Severin said he had offered to work as a consultant only because of a desire to share his knowledge.
"I never asked for money for tabling amendments," he told Reuters, calling the incriminating video a "fake" because it combined several conversations and presented them in what he said was a misleading way.
He said his work as a consultant did not break the Parliament's rules but conceded: "I don't say that perhaps I didn't commit any mistake. Maybe somewhere [...] it is something which is not absolutely correct."
Spoiling the Parliament's image
German MEP Martin Schulz, the leader of the socialist bloc in parliament, said the Romanian politician was spoiling the image of the EU assembly.
"Severin has held high-level positions in his own country and internationally and he knows very well what political and moral responsibility mean," he said.
"I hope that he will leave the European Parliament to prevent further damage to the institution."
Many of the European Parliament's members keep close ties or employment with industry during their five-year stint as legislators, a practice that is coming under scrutiny for possible conflicts of interest.
Former Slovenian Foreign Minister Zoran Thaler resigned on Monday and Austrian MEP Ernst Strasser stepped down on Sunday after the Sunday Times report was published.
Strasser was also shown in a video outlining his readiness to lobby for money. He has said he suspected a hoax and on Tuesday reiterated that no money had changed hands.
Thaler has said he was not involved in illegal activity and received no money, but was resigning while an investigation was conducted.
The president of the Parliament, Jerzy Buzek, has promised an investigation.
"Elected representatives of the people should know what is right and wrong," he said. "If the facts reported are proven, this type of behaviour is a serious breach of citizens' trust."
(EurActiv with Reuters.)