Ok if you are still under 6 months permanent they can dismiss you without cause as it is like a 'probationary' period. However this on applies to unfair dismissal, if it is unlawful (which discrimination is) then that is different. They can't do that.

You can ask to have a representative in the meeting with you and you can ask to have the meeting rescheduled to ensure that you representative is available. Call the union, get them to cal your boss and set the meeting time. Even if you aren't a member you can join on the spot and get representation. Don't go into the meeting alone!