Yup, had this exact fear during my IPO. Fortunately, stock went up, so it was a win that I was underwithheld.
I was and continue to be surprised companies release RSUs at IPO and not lock up expiry, the later of which avoids the tax risk.
I was and continue to be surprised companies release RSUs at IPO and not lock up expiry, the later of which avoids the tax risk.
Usually this results in significant underwithholding on RSU for federal tax.