The pages of the Italian passport offer a crash-course of sorts on high points in the country’s architecture. After the Pantheon in Rome and the Ducal Palace in Venice, page 31 shows a more modern structure: the cantilevered grandstand canopy of Florence’s main sports stadium, designed 90 years ago by the Italian architect Pier Luigi Nervi.

Immediately acclaimed for its avant-garde design, the reinforced concrete Artemio Franchi stadium is known to contemporary architects and engineers through countless textbooks on 20th-century architecture.

So, when the new American owner of A.C.F. Fiorentina, the stadium’s resident soccer team, announced this year that he wanted to tear the stadium down to build a more comfortable and modern venue for the club’s fans, architects and heritage associations went on the warpath.

Word of the threat got around fast among architecture guilds and university faculties. An online petition asking Florence’s mayor to save the stadium has been signed by heritage advocates as far away as Asia and Australia; ICOMOS, the France-based international agency that defends at-risk monuments and sites, has issued a heritage alert.

Last May, a committee of experts unanimously certified the building’s cultural and historical significance, bringing it under Italy’s strict conservation laws. But in September, the Italian government passed a decree designed primarily to streamline procedures for public works. The law included an article allowing sporting facilities, regardless of their historical importance, to bypass conservation requirements to make modifications — including reconstruction — that would improve a structure’s efficiency and bring it up to “international standards of security, health and public safety.”

Culture Ministry officials must identify specific elements of the sporting facility worthy of preservation: These can then be removed and conserved elsewhere, or reproduced, even in a different scale, the new law says.

“As absurd as it seems, the very people who were once tasked with protecting a monument are now called on to decide what to destroy,” said Elisabetta Margiotta Nervi, secretary general of the Pier Luigi Nervi Project Association, which was founded by the architect’s heirs to safeguard his heritage.

Italy takes the protection of its cultural heritage so seriously that it is enshrined in the Constitution. So conservators were immediately concerned when legislators approved measures chipping away at principles that seemed untouchable. Many fear that the law pushed through last September could be the first step toward dismantling Italy’s strict — and widely praised — conservation laws.

A.C.F. Fiorentina was bought in 2019 by Rocco B. Commisso, the billionaire chairman of the cable provider Mediacom. At the time, Mr. Commisso said that he was looking at what could be done about the team’s stadium, which undeniably lacks many of the bells and whistles of the arenas that are home to teams in Europe’s other top leagues.

Among criticisms of the design is that the seats on its curved sides are too far from the playing field; that it is only partly covered, so fans get wet when it rains; and that the retrofitted seats (it was designed as a standing-room stadium) are uncomfortable.

Most contemporary sports grounds include commercial areas with stores, gyms, restaurants, even museums that help teams defray their costs — but there are none of these in the 1930s Artemio Franchi stadium.

The building is owned by Florence city hall, which shares some maintenance costs with A.C.F. Fiorentina. A spokesman for the city, who asked not to be identified, as is common in Italian institutions, said that structural studies carried out with the University of Florence suggested that the stadium was showing signs of wear, “which is normal for a nearly 100-year-old building,” and that the building also required significant work to improve its security in the event of an earthquake.