Italy's Economy Minister Giancarlo Giorgetti told reporters the government would review the bid under rules designed to give Rome power to shield key assets
Italy's second-biggest lender after Sanpaolo Intesa has been pressing for a tie-up while Commerzbank has been honing its defence
Earlier this month, UniCredit took a 9 per cent stake in Commerzbank, catching German authorities off guard.
UniCredit shares jumped as much as 9.8% in Milan, trading at 12.65 euros as of 12:08 p.m.
The hurdles meant the two sides couldn't take forward a July agreement that the deal would be capital neutral for UniCredit and help the bank generate higher profit
The case stems from Santander's decision two years ago to suddenly drop plans to make Orcel its CEO after a disagreement over his pay package
In nearly five years at the helm, Mustier rebuilt UniCredit's capital reserves and cleaned up its balance sheet, but failed to find sustained profit drivers or lift the bank's depressed stock price
UniCredit's announcement triggered anger among unions in Italy
Contrary to expectations, shares of Italian banks including UniCredit have risen since December 4, the day of the referendum on the constitutional overhaul