Two German backpackers have been fined €950 ($A1513) and ordered to leave Venice for making coffee on the steps of the Rialto bridge.
The tourists, a man and a woman in their 30s, were arrested after a resident spotted them preparing coffee with a camping stove beside the Grand Canal, The Independent reported.
City officials said the Berlin pair contravened "the rules of public decorum and respect".
Public order laws in Venice, which receives some 30 million tourists a year, include bans on picnicking at certain sites and going shirtless in public spaces.
Venice mayor Luigi Brugnaro said: "Venice must be respected and those impolite people who come here and do what they want must understand that. Thanks to the local police, they will be sanctioned and removed."
Those who flout the rules will be reported to the embassies of their home countries, he added.
Venice recently introduced a controversial tax for short-stay visitors in an effort to ensure they contribute to the upkeep of the city.
Brugnaro announced early this year that tourists would be charged €2.50 from May 1, 2019. The fee will rise to €8 during high season and €10 during "critical" times when visitor numbers reach excessive levels.
"The aim is to improve the quality of life for residents," he said.
Venice has become the symbol of the problem of 'overtourism' - popular destinations that have become so overrun with tourists that it has made life difficult for locals.
In Venice, tourists far outnumber locals and a backlash has become apparent as ever more visitors arrive during the peak summer months.
The city's population basically peaked in the 1500s, and though it rallied again to near 16th century levels in the 1970s, today there are just one third as many Venetians as 50 years ago.
When a mammoth cruise ship rammed into a boat packed with tourists earlier this month leaving four injured, civic associations and the dwindling number of Venetians were quick to remind what they have been saying for years: the lagoon is too small and too crowded to accommodate the jumbo cruise ships that appear daily in high season.
Nearly 5 million tourists visited the city in 2017, compared with 2.7 million in 2002, according to data from the city's hotels, which do not take into account the thousands of bookings with Airbnb and similar services. Meanwhile, the resident population has shrunk below 60,000.