A restaurant in Venice that charged a group of Japanese tourists €1,143 (£994) for four steaks Florentine, a plate of mixed grilled fish, two glasses of wine and mineral water faces fines totalling at least €20,000 (£17,400), according to local media.

The La Nuova Venezia newspaper said police and local authority checks carried out at the Osteria da Luca near St Mark’s Square uncovered breaches of health and safety and food hygiene regulations, as well commercial code infringements including issues over the accurate description of goods.

“Together, the infringements – not all of which have yet been formally notified – produce total fines running into tens of thousands of euros,” the paper said. No grounds were found to shut the restaurant down, it said.

The Osteria da Luca – which has a rating of 1.5 stars on Tripadvisor, with 83% of reviews classed as “terrible” – faces further awkward questions from financial crime investigators over its failure to give the group a full receipt detailing their meal.

The four Japanese men filed a formal complaint with police after their return to Bologna, where they are studying Italian cuisine, offering as evidence the credit card slip that was the only proof of what the restaurant had charged them.

The mayor of Venice, Luigi Brugnaro, promised on Twitter this week that the city authorities would “thoroughly examine this shameful episode” and if it was confirmed, “do all we can to punish those responsible. We are for justice, always!”

A spokesman for the restaurant reportedly told journalists he had “no recollection of any problems with Japanese customers”.

Similar inspections at a nearby restaurant, the Trattoria Casanova, where three women in the same tourist group were charged €350 (£304) for three dishes of seafood pasta, uncovered no irregularities, La Nuova reported.

Trattoria Casanova, on the busy tourist route near St Mark’s Square, made headlines in November after a Birmingham family of three were charged €526 (£457) for lunch – including €297 for a platter of grilled fish. Italian restaurants commonly charge for fish by weight. The restaurant denied any wrongdoing.

In 2014, La Nuova Venezia said, a waiter from the same restaurant punched a Belgian tourist on the nose after the man complained about the quality of the steak he had been served, breaking his nasal septum and leaving him in hospital for a week.

The residents’ action group Gruppo 25 Aprile saw the most recent case as yet further evidence of the risk tourists run of being ripped off in Venice and took the Japanese tourists’ complaint to the police.

“We defend local residents, and whoever puts the good name of Venice at risk harms all Venetians,” it said. The Venetian Hoteliers Association this week offered a free stay to the group in a luxury hotel as a compensatory gesture.

“The association takes note of the fact that this episode has done grave harm to the image of the city,” Vittorio Bonacini, the association’s president, said. “After a high-level discussion, we’ve decided to offer the four tourists who had such an unfortunate experience a stay of two nights in a four or five-star hotel.”