The announcement by the center-right ministers came after Berlusconi urged ministers in his party to step down if the government doesn't revoke an increase to Italy's value-added tax that takes effect next week.
Tensions already were swirling around a Senate committee vote next week on whether to revoke Berlusconi's legislative seat because of the tax fraud conviction.
Letta, in a statement issued by his office, said Berlusconi was using the sales tax increase as an alibi "to justify the crazy and irresponsible gesture, all aimed only to cover up his personal affairs."
Letta said it was Berlusconi who was forcing the government's hand on the sales tax by depriving it of the stability needed to push through alternative measures.
"The Italian people will know to return to the sender such a big lie and attempt to distort reality," Letta said.
Democratic Party leader Guglielmo Epifani called the center-right ministers' move "irresponsible."
"They are provoking a crisis and we must evaluate exactly what the consequences are," he said.
Letta had warned on Friday that he will quit unless he receives prompt pledges of solid support in a confidence vote in Parliament on his government, which is struggling to pull Italy out of a recession.
Nearly all of Berlusconi's senators have vowed to quit, if a Senate committee votes next week to strip him of his Senate seat because of the conviction.