Tensions between the union representing firefighters in Pawtucket and the city administration are boiling over into public view. The union, IAFF Pawtucket Firefighters Local 1261, filed a grievance last week after an assistant chief was suspended for two days over his refusal to change a report about another firefighter who was badly injured on the job. Mayor Donald Grebien, meanwhile, put off a political fundraiser he had planned for Monday at the Pawtucket Country Club because the union had planned to picket it. “Unfortunately, the fire union bullies mayors statewide as they protect their residents they are elected to serve,” the statement said. “We will not provide the fire union this opportunity to intimidate those planning on attending the fundraiser.” The two sides are not only fighting, they’re fighting over what they’re fighting about: The city says the planned protest was much ado about contract negotiations, while the union says it’s raising concerns about safety for its membership and the people of Pawtucket.