I am not a tax person or a stock person, but what I have been told at the start-ups I have worked at, you have to wait 6 months after an IPO before you can sell

I am not a tax person or a stock person, but what I have been told at the start-ups I have worked at, you have to wait 6 months after an IPO before you can sell or something along those lines. So, yes, the employees can sell their stock, but not right now. They didn't get the chance to sell at the potential high.