Can an employer have different rules for different sets of employees?

ERISA requires pension plans to provide for vesting of employees' pension rights after a specified minimum number of years and to meet certain funding requirements. It also establishes an entity, the Pension Benefit Guaranty Corporation (PBGC), that will provide some minimal benefits coverage in the event that a plan does not, on termination, have sufficient assets to provide all the benefits employees and retirees have earned. Later amendments to the Act require employers who are withdrawing from participation in a multiemployer pension plan that has insufficient assets to pay all of employees' vested benefits to pay their pro rata share of that unfunded vested benefits liability.