The employees can apply for a temporary work visa which can be for up to 4 years and is tied to a particular employer which is required to sponsor the temporary worker.
There is a permanent employer nominated scheme visa which is also tied to the sponsor during the sponsorship and the visa processing stage but once the employee arrives in Australia the employee is independent to seek employment elsewhere subject to fulfilling the obligations the employee has under any employment contract between the employer sponsoring the employee and the employee and the employer fulfilling its obligations.