Asking employee to pay for H1B filing is illegal in US. If you have a solid proof and want to sue them, you can do in the court of law. Before that, to avoid any lay-off from current company as you are working under H1B, transfer the H1B to any other company first and sue the first one if its a big amount. Otherwise, remember once you are in lay-off, after few weeks of grace period, you will be out-of-status. Think wisely.