If you have been sponsored for a 457 visa and wish to leave your employer, your employer is obliged to inform Immigration once you have terminated your employment contract. You will then have 90 days time to transfer to another employer or apply for another visa. Once the 90 day period is up, you will receive a notice from Immigration informing you that they plan to cancel your visa. For employer-sponsored permanent residency visas, you are required to declare that you will work for your employer for at least 2 years.