(Adds opposition reaction, details)
NIAMEY, Aug 27 (Reuters) - Lawmakers in Niger voted on Wednesday to lift the immunity from prosecution of the president of parliament, a key opposition leader, so he can be arrested on suspicion of involvement in a baby-trafficking network.
Seventeen people, including the wives of several senior politicians, were arrested in June by police investigating allegations they acquired new-born babies from "baby factories" in neighbouring Nigeria.
The second wife of parliament speaker Hama Amadou, a former ally turned political rival of President Mahamadou Issoufou, was among those detained in the affair.
Political tensions have risen in Niger since last year when Amadou, who had been part of Issoufou's coalition, fell out with the president. Issoufou's government has accused Amadou and his Nigerien Democratic Movement (MODEN) party of trying to incite a military coup in the uranium-exporting West African nation.
The government introduced a request with the parliament on Tuesday, asking for his immunity to be rescinded.
"We have authorised the judicial authorities to question and arrest the deputy Hama Amadou," said Daouda Malam Barte, the vice president of the National Assembly.
"It is not with a light heart that we have decided this. But the government has itself handed over one of its ministers this weekend. There is a separation of power in Niger," he said.
Niger's Agriculture Minister Abdou Labo, one of the most senior figures in the government, was arrested on Saturday over his suspected involvement in the alleged trafficking ring.
The decision to allow Amadou's arrest was taken by the members of the parliamentary leadership. Amadou did not attend the meeting.
Amadou has said the investigation is politically motivated, and his allies in the National Assembly criticised Wednesday's decision.
"The constitution has been violated. A deputy cannot be arrested without his parliamentary immunity being lifted and that is done in a full session of the National Assembly," said Tidjani Abdoulkader, a leader of the opposition in parliament.
(Reporting by Abdoulaye Massalaki; Writing by Joe Bavier; Editing by Daniel Flynn and Emma Farge, Ralph Boulton)