Italy's Deputy Prime Minister Matteo Salvini said Tuesday he expected Brussels to slap Rome with a €3 billion fine over the country's rising debt and structural deficit levels.

"At a time when youth unemployment touches 50 per cent in some regions... someone in Brussels is demanding, under the old rules, a fine of three billion euros," he told RTL 102.5 radio.

"All my energy will go into changing these rules from the past," said Salvini, whose far-right League party won Sunday's European Parliament elections in Italy.

"We will see if this little letter from Brussels in which they sanction us for debt accumulated in the past arrives," he said.

The European Commission is expected to start disciplinary steps against Italy on June 5 by opening an excessive deficit procedure which could hand Italy a fine of up to 0.2 per cent of the nation's GDP.

Italy's public debt is a big problem, sitting at 132.2 per cent of the country's GDP in 2018 - way above the 60 per cent EU ceiling.

The League and its Five Star Movement coalition partner rowed bitterly with Brussels at the end of last year over their big-spending 2019 budget, which the European Commission rejected in a historic first.

Both sides then made compromises to get the budget over the line.

But in the Commission's latest economic forecasts, published in early May, Italy is ranked as the eurozone's worst performer, with growth well below other countries and debt at a record level.

Brussels is set to send a letter to Rome on Wednesday calling on the government to explain itself, a European source said.