(adds govt calls confidence vote on amnesty)
ROME, Sept 29 (Reuters) - Italy's planned tax amnesty to bring back to the country undeclared funds held abroad could harvest 300 billion euros, the state revenues agency said on Tuesday.
Italians have an estimated 125 billion euros held in Switzerland and 86 billion euros in Luxembourg, the agency said in a statement.
The amnesty, which is due to be approved by parliament this week, would allow Italians to avoid prosecution for previously undeclared funds by paying a 5 percent penalty.
It offers Italians "a last chance to regularise their position", the agency said.
The Italian government later on Tuesday called a confidence vote in the lower house of parliament to speed up approval of the measure.
The centre-left opposition and Italy's largest union have attacked the proposed amnesty, which wipes the slate clean on offences including accounting fraud for money hidden abroad.