Why has your company not sent you to Australia? Is there a specific clause in your appointment that prohibits overseas assignments?
If your employer's business requires you to be sent anywhere in our country or abroad, the company should be able to do so, in my opinion. However, the company should compensate appropriately for any disruption to your personal, family, and social life.
The 457 Visa
The 457 visa is a Temporary Work Visa (Subclass 457). In Australia, the 457 visa was commonly used by Australian or overseas employers to sponsor skilled overseas workers for temporary work in Australia. This visa has now been abolished and replaced with the entirely new Temporary Skill Shortage (TSS) visa as of March 2018.
It is important for you to familiarize yourself with the TSS visa.
If you refuse to go, your employer may need to consider finding someone else for the position, potentially leading to your role being deemed redundant. Please take this into consideration.
Kind regards, [Your Name]