"We cannot resign ourselves to the idea of ethnic replacement: Italians have fewer children, so let's substitute them with someone else. That's not the road to go down," Lollobrigida said during a congress in Rome.
Lollobrigida is a senior member of far-right Brothers of Italy party, as well as being Meloni's brother-in-law, and his comments were slammed by opposition parties.
Critics say Meloni's coalition, which includes Matteo Salvini's far-right League party, has been fueling anti-immigrant sentiment in Italy.
Some 32,700 people have landed so far this year, compared to 8,400 in the same period last year - a increase which prompted Meloni's right-wing coalition to call a six-month state of emergency last week.
The left has repeatedly accused the government of undermining rights.
Elly Schlein, head of the center-left Democratic Party, said they were "disgusting words" that have "a flavor of white supremacism about them".
She noted that Lollobrigida made the comments while Italy's president Sergio Mattarella was attending a memorial at the Auschwitz concentration camp in Poland.
Auschwitz-Birkenau has become a symbol of Nazi Germany's genocide of six million European Jews, one million of whom died at the camp between 1940 and 1945 along with more than 100,000 non-Jews.