
Nattapong Suwannarat claimed that a Siam Ruamjai supervisor gave his men the order to "get them all".
Nattapong said the two groups had agreed on separate territories to assist accident victims, but Siam Ruamjai had begun stealing the Foundation's jobs.
Pol Maj Gen Sakkachat Kittikajorn said that after dealing with the attack, police would call in rescue foundation chiefs for talks.
The trouble follows an incident between the same groups on September 27, near Soi Ramkhamhaeng 60 in Bang Kapi district, which left two injured and five trucks damaged.