Whatever you do, don't contact the women in question, and don't fcuking lose your temper when getting called in tomorrow.
Be the nicest guy in the world, but deny everything. Don't make any accusations, just stick with what happened and nothing else.
If there is a union representative at your work, you could talk to them, or call the local union rep, they're always interested in fighting those kinds of fights I suppose.

Just don't lose your cool, and don't sign anything.
Best thing you could do probably, is to get ask the boss for one or two more days to look at what you're charged with, since your job is on the line.
Then contact the union. I doubt this situation is grounds for dismissal actually.
Especially not since you're denying ever saying it.
Good luck.
YIP
Zack