If you are called into any meeting that could lead to discipline, you may request an association representative before answering questions. Say it plainly: “I request association representation.” Then stop talking until a rep is with you.
A request for a statement and an order to give one are different things, and the difference decides your rights.
If you are ordered to give a statement about something on the job, you are being compelled under threat of discipline. Comply — but first ask the supervisor to confirm it is an order. Then tell them you intend to comply and want to confer with legal or union representation. A compelled statement carries Garrity protection (Garrity v. New Jersey): because the government is your employer, your Fifth Amendment right against self-incrimination survives, and the compelled statement cannot be used against you in a criminal case.
If the supervisor says the statement is voluntary, contact a rep immediately. People give voluntary statements because they believe they have nothing to hide; take the right to remain silent seriously anyway. If you feel pressured to give a "voluntary" statement, note who pressured you and when — that may itself make it compelled.
Add this paragraph to the top of any compelled written statement. Fill in the blanks.
On ________ (date/time) at ________________ (place), I was ordered to give this statement (report) by ____________________ (name/rank). This statement is being compelled as a condition of my employment with the Department. I understand that I may face disciplinary action for disobeying this order so I have no alternative but to abide by the order. It is my belief and understanding that the Department is compelling this statement (report) solely and exclusively for internal purposes and will not release it to any other person or agency. It is my further belief that this statement (report) will not and cannot be used against me in any criminal proceedings. Further, I rely specifically upon the protection afforded me under Garrity vs. New Jersey 385 U.S. 439 (1967).