they can change your contract subject to given you sufficient notice, dont sign, and you effectively saying i resign
Ive been in similar situations before, after we changed companies, they all gave us a new contract to sign, to make us work 30 min longer a day, for no extra pay, 2 months later, and those who hadnt signed, didnt have jobs anymore.
but another company, when we were bought in line with the parent company, we signed a contract saying to work 30 min less a day, but loose one days holiday a year instead, swings and roundabouts,
talking of which, ill be moved across to a new company 1st of april, (if havent been laid of by then) and then it will be a whole new ball game