Two Austrians have been arrested, as well as a man in Belgium who was believed to be the fence for the stolen goods, and three men in the Netherlands.
Investigations are still ongoing in the Netherlands and Belgium, said Rudolf Frühwirth from the Upper Austrian police.
Austrian police began investigations last year after a 43-year-old Lower Austrian man was stopped at a checkpoint in Upper Austria, with what turned out to be a stolen tractor on his trailer. Eight similar vehicles were then discovered on his property.
When detectives investigated the man they found that he had bought 26 agricultural vehicles between September 2012 and May 2013 for several hundred thousand euros, and then sold 18. All the vehicles had been stolen in the Netherlands or in Germany and had fake chassis numbers or nameplates.
An Upper Austrian man had bought six vehicles from the same source on the Internet.
In the Netherlands police seized devices used for manipulating the chassis.
So far 28 stolen tractors have been returned to their rightful owners, but the group is likely to have stolen and sold many more.