The People of Freedom Party, or PdL, issued the warning to the center-left Democratic Party, or PD, which wants to hold regional elections at a separate time, Italy's ANSA news agency reported.
Holding regional and national elections at different times would cost an additional $128 million in "tax," said Angelino Alfano, PdL secretary.
If PD did not end its opposition to a single election, Alfano threatened to drop support for the party, which could cause the government of Prime Minister Mario Monti to collapse.
Alfano said Monti's Cabinet could decide at Friday's meeting if the elections should be held on a single day.
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