1) Only the company you are working for at the time you are injured (i.e. the one whose job you are doing then) may be liable. Liability for a work-related injury is based on the employee doing a job for the employer at that time and being injured in the course of employment--just being employed by another employer, or having both employers housed in the same building, does not make the one you are not then working for liable.2) If an employer does not have worker's compensation, you can sue it for the injury; they are not protected from lawsuit by the worker's compensation laws (under which you get the worker's compensation in lieu of suing).