That doesn’t sound like a good idea at all. The union is there to represent it’s workers not set prices. If the company finds itself entirely unable to pay the increased wages and benefits without raising prices then those prices were artificially low by taking what the actual cost should have been and subtracting how much they were screwing out of their employees.
If there is money available to pay for the increased cost of their workforce in the form of reduced executive benefits or pay, then they should either do that, or not, but suffer a market penalty for having more expensive cars than their competitors. If it starts really hurting their bottom line then they’ll have to make some actual tough decisions about compensation at the top like the “tough decisions” they pretend to have to make when they announce wage cuts and lay offs.
While unions are great, they are and should be entities for a specific purpose and it doesn’t make sense for them to be expanding beyond that. They’re not charities or NGOs representing just general social good, they’re specifically about pay and conditions for the workers they represent which hopefully will translate to a lot of social good in general. If for example there are many strong unions across all sectors with most workers as part of one then consumers would have some actual money to buy a car at a fair price that reflects the costs of labour. Where this happens, big companies don’t pack up and leave despite constantly wailing that they will, because there’s obviously still money to be made but the environment is such that their options for profligacy are greatly constrained and they have to operate with some sanity.