The clash took place between the groups owing allegiance to sitting SAD MLA Joginderpal Jain and former Punjab DGP P S Gill for taking control over the Moga truck union, they said.
Police intervention brought the situation under control, they said, adding that two of the three injured were in serious condition.
Both the groups accused each other of pelting stones and firing in the air, police said.
Alleging that Jain's followers opened fire on them in which Harnek Singh received serious injuries, Gill's supporters blocked national highway for two hours seeking action against them.
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During the clash, Gill was not present while Jain was at the spot.
Heavy police force had been deployed in Moga city in advance as it was apprehended that the two groups might clash with each other, police said.
The situation is under control and the matter is being probed, they said.