Anything that's too tight or narrow is constricting. Face it, your pants are a size too small — you should change into something less constricting.
When something is constricting, it puts pressure all around, like a constricting blood pressure cuff squeezing your arm. A constricting belt might need to be let out a notch, and a constricting necktie ought to be loosened at the end of the day. When something is figuratively constricting, it inhibits your freedom to do what you want: "The constricting dress code at school meant she couldn't wear her favorite hat."