Police in Sicily say 15 firefighters are suspected of setting blazes that they were then called to extinguish.
The Mediterranean island in summer is often by plagued by arson fires.
Police in Ragusa said the head of a firefighting squad was put under house arrest and the others under investigation.
Auxiliary firefighters like them receive 10 euro (£9) per hour from the Italian government to fight fires.
Police said fire department officials tipped authorities off that one team of auxiliaries was called far more often than others to work in summer 2013 and 2014.
The ANSA news agency said some are also suspected of calling in false alarms.
This summer, several arson fires have raged in Sicily and much of central and southern Italy, amid a drought and heat wave.