It sounds like the employer is pushing for this, for whatever reason.
Most likely reason is to have labor peace in their other plants. Rather than letting themselves being pitted against each other, European workers have a better track record on colluding for their common interests than American workers do.
VW has a long-standing and positive experience with plant-level agreements, especially with respect to working hours. They have, e.g., introduced models that allow workers to build up overtime accounts, which will be used to work under time at no wage loss in periods of low capacity utilisation / demand. Such agreements are accompanied by long-term job guarantees (no lay-offs during crisis).
VW, as other German car manufacturers, tends to invest heavily into staff training in order to maintain quality, and has no interest in losing that human capital because of temporary sales drops and subsequent lay-offs. For such agreements to be concluded and work, they need an accepted plant-level negotiation partner on behalf of their employees.
I also guess they expect positive PR in the US. If I was in charge of VW's marketing, I would try to capitalise on the buggy / VW bus "hippieish" image, and such a target group should be quite sympathetic to VW increasing and strengthening labour rights..
