Offenses included squeezing too many beds into rooms licensed for less, the Italian news agency Ansa reported on Friday.
One 15-bed hotel was found to have squeezed in 24 beds, the agency said.
Others are also being investigated for failing to hand over nightly room taxes collected from guests.
Italy's interior ministry said on Wednesday it is expecting 19 heads of state, 24 heads of government and 800,000 pilgrims in Rome for the sainthood ceremony of popes John XXIII and John Paul II.
The result of the arrivals has also been visible in rental prices, with the web portal Casa reporting the average for a furnished flat being rented out for the canonisation weekend up between 137 and 173 percent from previous weekends.
The mayor's office is awaiting 4,300 coaches and there were will be special trains and flights to the city.
Some pilgrims will even arrive by boat to the port of Civitavecchia near the Italian capital.
"From Poland alone, we are expecting 1,700 coaches, 58 charter flights and five special trains," said Maurizio Pucci, an official from Rome city hall, adding the canonisation will put the city under "stress".
The interior ministry will deploy 2,400 security officers and there will be around 2,000 extra local police officers in the streets.
Law enforcement are also expecting an influx in pickpockets from across Italy to take advantage of the concentration of foreign tourists.
For the period of the canonisation, the city's plan is to boost public transport with extra buses on Saturday and Sunday and run the metro system around the clock.
Nineteen giant screens are being set up around the city to follow the ceremonies in different languages including Arabic, French, Italian, Polish and Spanish.
St Peter's Square will be closed to pedestrians on Saturday and access for pilgrims to the ceremony will only begin on Sunday at 5.30am (0330 GMT).