The "Mare Nostrum" (Our Sea) operation, launched last October, plucks people from floundering vessels in the Mediterranean almost daily, at a cost of €9 million a month according to Italian media reports.
"This expensive and maniacal operation must be immediately stopped," said Maurizio Gasparri, a former minister from the centre-right Forza Italia party, describing Mare Nostrum as "a taxi...with people smugglers alerting the Italian navy, which then brings in endless numbers of illegal immigrants."
The government has warned that the landings are set to increase, estimating this month that up to 600,000 migrants from Africa and the Middle East are ready to set off from Libyan shores.
Matteo Salvini, head of the anti-immigration Northern League party, has also called for the operation to be scrapped, saying "Italian citizens end up financing the people smugglers and an invasion of our coasts."
The arrival in Sicily on Tuesday of 321 migrants, including 62 women and five children, brought the number of people saved over the past 48 hours to 1,149 according to the navy, which did not specify their nationalities.
Close to 22,000 migrants and asylum seekers have arrived on Italy since the start of the year, 10 times the number in the same period in 2013.
On average, five military ships and 900 sailors take part weekly in the rescue operation.
Immigration charities estimate between 17,000 and 20,000 migrants have died at sea while trying to reach Europe in the past 20 years, but fighting the phenomenon from both Africa and Europe has proved difficult.
Last week, Italy joined six other European Mediterranean nations in calling on the EU to boost financial support for those bearing the brunt of the influx of African migrants in search of a better life.
Migratory pressure pushing across the Mediterranean "is far from diminishing, it is increasing", said foreign ministers from Cyprus, France, Greece, Italy, Malta, Portugal and Spain after an informal meeting in the Spanish port of Alicante.