As a for instance, employers will(illegally) demand that the H1B worker reimburse them for the legal and filing fees as a form of retribution for transferring. While certain greencard sponsorship related expenses can be recouped if the H1B is that far down the line, any visa related costs (attorney, filing fed) must be payed for by the sponsor.
https://www.dol.gov/wecanhelp/h1bworkers.htm