I've had the opposite experience. I once was offered an unfair equity package from cofounders of a startup. I (and two others) wrote up a document voicing our unhappiness and the reasoning behind it.

And they ended up agreeing with us. While the offer they first came up with was not fair to us, they honestly hadn't realized it (they had a lot on their minds, it was the first solution that came to them, and they simply proposed it).

We did not poison our relationship. They agreed that our solution was more fair (it involved each of them getting less equity and each of us getting more, by the way). And, in the end, the company had a (modestly) successful exit.

We are all friends to this day.

OP: If it's unfair: write down why it is unfair and what you would propose as a more fair agreement. Only if and when they reject that should you involve an attorney. But there is absolutely a chance that they will realize your solution is better.