Can employer start year with diff. contribution rate (ins) for new hires?

company has historically paid 100% of employees healthcare costs (individual up through family) typical HMO plan. There are defined upcharges which the employee does cover for plan upgrades. With continued rise in costs we are looking at two things:
1. Charging employee for spouse coverage if spouse is working and has health care available to him/her.
2. Looking at introducing different plan for new employees hired in 2012 where employee contributions would be standard. Can we legally do so (therefore grandfathering in current employees)?