If this person is supposed to be working, and instead attends a tea party, I can understand why that would be a problem, just as I would not skip work to go to the library or register to vote. If the person has the day off, they are free to participate in such a gathering if they so desire. DHS would have a nice lawsuit on its hands if it attempted to interfere with an employee’s legal off-duty activities. There is not enough info in this posting to determine exactly what happened.
That was my thing as well. Take a day of vacation, or a couple of hours vacation if you place work that way. Attend the party on your time. I wanted to attend the one here but I have to work, and going in my uniform is frowned upon.