People of Italian descent have for decades been able to dig through their family trees, find an Italian ancestor and apply for citizenship to Italy, securing a powerful passport that allows them to enter more countries without a visa than travelers of almost any other nationality.

But so many have tried to claim the benefit that their applications have congested Italy’s courts, consulates and municipal offices, grinding other work to a near halt.

The government has had enough.

Fewer people of Italian descent will now be able to obtain citizenship after the government narrowed eligibility only to those with Italian parents or grandparents.

The decree, announced on Friday and effective immediately, strips away a provision that had allowed all comers to seek citizenship if they could prove — often through a lengthy and laborious process — that they had an Italian ancestor who was alive after the country was formed in 1861.

Antonio Tajani, the Italian foreign minister, said the stricter regulations followed “years of abuses” by people who had few ties to the country and only coveted its passport.

Italy has granted citizenship in recent years to a surging number of South Americans, Mr. Tajani said, suggesting that many new Italians mainly hoped to travel around Europe or to the United States. “Being an Italian citizen is a serious thing,” he said at a news conference. “It’s not a game to get a passport in your pocket to go shopping in Miami.”