Why are there separate entrances for union and non-union workers at a local construction site?

The title pretty much says it all. A building is going up a few blocks from me, and the construction site is all fenced in. It seems like there are two entrances, because the one I can see from the side I usually drive past says "Entrance B: Non-Union." I'm assuming there's another entrance is around the other side.

So...any one know why this might be?

Perhaps there was trouble between the two groups in the past, and this is the only way to keep them apart so they don't fuss.

Regards,
Shodan

Quote:

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Originally posted by Shodan

Perhaps there was trouble between the two groups in the past, and this is the only way to keep them apart so they don't fuss.

Regards,
Shodan

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This was my only guess too. I hope someone that knows has an answer.

Maybe there are different time clocks and people to report to?