The latest attack happened on Alder Street at about 10.40pm on Saturday June 7 where two minibuses parked on the car park at Atherton Collieries Football Club were set on fire.
Plastic containers containing some sort of accelerant were thrown at the vans starting the blaze.
This is the third attack in the last two months and the Probation Service is offering a reward of £1,000 for information that leads to the arrest and conviction of whoever is responsible.
A probation office on Warrington Lane, Wigan, was severely damaged following an arson attack at about 9.50pm on Sunday May 11.
It is believed that two men forced their way into the premises with two barrels of petrol and started the blaze.
No one was injured as a result of the fire, however the building suffered extensive damage.
Police are working on the theory that this incident could be linked to another arson attack at the National Probation Service on Gloucester Street in Atherton on Sunday April 27. On this occasion those responsibleclimbed over the fence between 8.15pm and 9.20pm, and set fire to three vans in the car park
Det Sgt Graham Rigby from Wigan CID said: "We are now dealing with three arson attacks and although no one has been injured, the potential for fires to get out of control easily means the attackers obviously have no regard for the safety of others.
"At this stage I am linking these attacks and appeal for anyone that may have any information that could help my investigation to come forward before someone is seriously hurt."
Anyone with any information about either incident is asked to call Wigan CID on (0161) 856 5307 or Crimestoppers anonymously on (0800) 555111.