A French couple who were caught with 40kg (90lb) of Sardinian sand in their car could face up to six years in jail.
They say they wanted to take the sand home as a "souvenir" and did not realise they had committed an offence.
Sardinia's famed white sand is considered a public good and it is strictly forbidden to remove it from the island.
The couple face a jail term of between one and six years for the crime of theft with the aggravating circumstance of having stolen an asset of public utility.
Under a 2017 law, the trade in sand, pebbles and shells is illegal, and usually punishable with fines of up to €3,000 ($3,330; £2,750).
Police discovered the sand crammed into 14 plastic bottles taken from the beach in Chia, southern Sardinia, in the boot of an SUV belonging to the couple.
They were about to board a ferry in Porto Torres heading to Toulon, France, reports say.
In 1994, access to the renowned pink beach on Budelli island to the north-east of Sardinia was banned amid concerns about its future.
The authorities are concerned as several tonnes of the island's precious sand disappear every year.
"Sandy beaches are one of the main attractions of Sardinia. There are two threats: one is due to erosion, which is partly natural and partly induced by the increasing sea level due to climate change; the second is sand stealing by tourists," Pierluigi Cocco, a resident of the Sardinian capital, Cagliari, and environmental scientist, told the BBC.
"Only a fraction of the tourists visiting Sardinia spend their time digging up to 40kg of sand each. But if you multiply half that amount times 5% of the one million tourists per year, in a few years that would contribute significantly to the reduction of beaches - the main reason why tourists are attracted by the island of Sardinia."
Tourists, mainly Europeans and including some Italians, bottle the sand up to then auction on online sites.