Say a person works for an employer for 2+ years based on the statement (promise?) that they will be 100% vested in their 401k employer match after 5 years. Is the employer then permitted to change the rules so that it will take the employee 6 years to be fully vested?
From my research it seems they may be allowed to do this provided they don't reduce the percentage already vested at any point? However even given that, it would still seem unfair since the job would have been partly been accepted based on the original promise, and when the vesting schedule is made worse, then at the point it's made worse, it's like telling someone, hey that money you have been anticipating (and working under the assumption) to be fully yours by year 5 will now take until year 6 to be fully yours.
EDIT: I just found the following guidance on the IRS website
Seems from this link (esp. the example they offer) that there are actually quite tight restrictions on what employers can do... e.g. seems to me that if accrued non-vested amounts are additionally restricted by a worsened future vesting schedule, that this may not be allowed after all? And even for people with less than 3 years service?!