Be sure any unfunded withdrawal liability related to the pension is booked on the balance sheet (there is almost always underfunded liability). Depending on the amount, I've seen situations where the seller is willing to divest for only the assumption of the liability (assuming the liability is close to EV). It's very inexpensive financing.

Consider partnering with them. Also out of the box idea would be to offer the employees some of the equity within the deal (maybe through a phantom equity grant check out redacted) that way the fight is not with ownership or management (since they would in fact be the former and be served by the latter) rather with the market and critiquing the business plan. My experience is that with the right approach unions can be catalytic within a business and could even be a true partner DURING the search phase. It's just all about setting up the right incentives.