The new restrictions came into effect at midnight last night.
Acting premier and state health minister Roger Cook, described the situation in Victoria as "devastating" but said the measures that have allowed the state's economy to reopen had to be strengthened and protected.
The exemptions previously allowed to FIFO workers to enter the state from Victoria have now been revoked, meaning only specific essential workers, such as transport and freight workers and those approved by the State Emergency Coordinator, would be permitted to enter WA.
"WA's hard border with the east is working in that we have reduced the number of arrivals by 98% of what we would normally expect pre-COVID," Cook said.
"However now is the time to bolster our COVID-19 measures further to better safeguard Western Australians - and that's what we're doing."
Those who are permitted to enter WA who have been in Victoria for the previous 14 days will be compelled by state authorities to take a COVID-19 test on Day 11 or at any point when symptoms develop.
Those who refuse will face a A$5000 fine.
An Australian Petroleum Production and Exploration Association spokesman told Energy News many Victoria-based workers fulfil key roles at WA's oil and gas operations.
"We are currently working with industry to ascertain the number of Victorian residents critical in the operation of local facilities, and will then apply to the WA Police Commissioner for an exemption on a case-by-case basis," the spokesman said.
While the bulk of Chevron's workforce is WA-based, Inpex, Woodside and Shell's operations in the state rely on interstate FIFO-workers, as does Jadestone's.
"We are currently working through the government's latest changes," a Chevron spokesman told Energy News.
"Our priorities will continue to be the health and safety of our employees, contractors and the community, as well as maintaining vital supplies of natural gas to Western Australia and the region."
A Woodside spokesperson said the company was "currently assessing the impact of the state government's announcement".
An Inpex spokesperson said the company was "considering the changes".
Pre-COVID, there were around 520 FIFO workers across the mining, oil and gas sector from Victoria working in WA, according to the state's Chamber of Mines and Energy.
A CME WA spokeswoman told Energy News that it was hard to track what that number was now, given so many companies had changed their rosters so quickly to deal with the restrictions.
She said it was too early to tell at this stage how the latest restrictions would affect companies' operations.
A Shell spokesman told Energy News most of its FIFO workers who would have been impacted have been relocated into WA.
"We continue to monitor closely to ensure the well-being of our staff and contractors, and follow the advice of the relevant authorities," he said.
"Where we have individual workers impacted by the travel restrictions imposed by the relevant authorities, we will work with those workers on an individual basis to discuss alternative arrangements."
A spokesman from union coalition group, The Offshore Alliance told Energy News this morning that Victorian based workers had been understanding about the state's call.
"They're concerned about potential loss of income and ability to work, but none have criticised the action of the [WA] government - obviously we need to keep WA free of COVID -19," he said.
Victoria this morning recorded 288 new cases of COVID-19.
