First of all, any employer is allowed to swap one Retirement Plan for another. There is (in all likelihood) no deemed Termination of the Retirement Plan that would justify you taking a Distribution of what you had in your old Plan.

Second, when you state that the new ("Successor") Plan has worse benefits than the old Retirement Plan, there are regulations that require you to NOT lose any of the benefits acquired while under the old Plan. This includes your account balance and Vesting percentage, among other benefits.

Thirdly, I'm not surprised that they are replacing the Union's Retirement Plan, thus leaving the corporate Plan alone. This is usually the place where you and your co-workers get ahold of the Union leaders and ask that they start pushing management to better hear your and your co-workers' disappointment with the new situation.

If you are looking for more qualified help, I might suggest seeking out an individual with the ERPA (Enrolled Retirement Plan Agent) designation (or something similar) - such a person is likely to have a better grasp of Employer Retirement Plans and what is and is not allowable.

Good Luck with getting the most out of your upsetting situation!