The deceased was identified as Hadiuzzaman Russel, 28, general secretary of Koyra upazila BCL unit.
Md Abu Sayeed Khan, vice-president of Khulna district BCL unit, said Russel succumbed to his injuries around 6:10 am while he was being taken to Dhaka for better treatment.
According to locals, three brothers Tuhin Hossain, 40, Babu, 37 and Milon, 30, sons of Hafizur Rahman, forced workers to stop wielding work of the under-construction bridge on Batikata canal in Bailharnia area around 11 am on Sunday.
Later, the issue was dissolved with presence of local influential people.
Later, when Russel along with his supporters went the spot around 4pm, Tuhin along with his brothers and supporters attacked them which ensued the clash between the two groups.
At least eight people of the two groups, including Russel, were injured in the clash and after primary treatment at Koyra Upazila Health Complex he was sent to Khulna Medical College Hospital.
As his condition deteriorated he was referred to Dhaka.
Rabiul Hasan, officer-in-charge of Koyra Police Station, said police arrested Tuhin and Milon from the spot.