Permanent to temp?

[loadthetoad]

I'm returning to work in October after a year's maternity leave.
I've asked to go part time to 0.8 which has been granted but they want to change my contract to temporary. Can they do this? I'm a teacher and this has happened to 3 TAs in school (new head who would prefer all full timers) one left and the other two went to full time.
I will contact my union tomorrow but had the conversation earlier this evening and now I'm panicking about my job security.

How long have you been there? I think they can issue you a whole new contract for 0.8 which is temporary and 1.0 which is permanent. What did the union say?

I have had a temporary adjustment to my contract to 0.6 in the past. It just meant that they could make me full time again after two years.