Italy's regional affairs minister Enrico Costa resigned on Wednesday amid dispute over a hotly contested bill that grants Italian citizenship to the children of immigrants.
Costa, who is from the government's junior coalition partner, Alternativa Populare (AP) a small centrist party, said in a statement that a conflict between his "role" and his "beliefs" had emerged in recent weeks.
Italian prime minister Paolo Gentiloni has taken on the regional affairs portfolio on an interim basis.
Costa had threatened to quit if the citizenship bill and one on the reform of criminal trials went ahead.
His party is crucial to the government's survival in the Senate, where it has a slim majority, and after objections from AP, Italian prime minister Paolo Gentiloni delayed a parliamentary vote on the citizenship bill until the autumn.
But Gentiloni said on Tuesday the bill was still a priority, signalling that the underlying disagreement with AP was unresolved.
Foreign minister Angelino Alfano, described Costa's resignation as "inevitable and tardy". "I thought he'd do it a few days ago," said Alfano.
Costa, who left billionaire media magnate Silvio Berlusconi's conservative Forza Italia party in 2013 to join what is now AP, is expected to return to Forza Italia, in a sign of the 80-year-old former premier's returning political influence.
According to the proposed law, children born in Italy to non-Italians, or who arrive before their 12th birthday and spend at least five years in formal education, could be declared citizens.
One of the children's parents need have a long-term residence permit before they can apply for citizenship, under the long-delayed bill, to which opponents have tabled 48,000 amendments.
Immigration is one of the most controversial issues facing politicians in Italy, where over half a million foreigners have arrived in the past three years, mostly sub-Saharan Africans who landed by boat from Libya.
