Police officers and staff are required to have their first vaccine dose by December 1 given they are classified as critical workers by the state government.
Those who do not comply will be blocked from entering police stations or other facilities.
WA's police union says members have been told they will have to use their leave allowances or go without pay if they fail to meet the deadline.
"That's obviously annoyed us as a union," acting president Mick Kelly told Perth radio 6PR on Monday.
"We've been advocating that our members don't have their pay cut ... and maybe find alternative work locations.
"It's tight out there as it is. We need to retain as many officers as we can."
Several hundred WA Police employees were yet to provide proof of having had their first dose.
Mr Kelly said 150 officers were currently on leave but only 20 had indicated in survey responses they didn't intend to get vaccinated at all.
In written advice to the state government earlier this year, WA Chief Health Officer Andy Robertson said police officers were placed at a high risk of exposure to COVID-19.
"Due to the WA Police Force comprising a very large workforce, their close interaction with the community, the unpredictable nature of the work they do, their interaction with vulnerable communities and the broader public health impact of that work, there is a strong public health benefit to mandating COVID-19 vaccination for the entire workforce," he wrote.
WA Police employees are required to be fully vaccinated by January 1.
The McGowan government has introduced broad-reaching vaccine mandates, affecting about 80 per cent of WA workers, as it prepares for an influx of cases when it reopens domestic borders in late-January or early-February.
Mark McGowan has faced backlash from anti-vaxxers, some of whom have levelled death threats against the premier and his staff.
Police on Sunday were forced to hold back a crowd of protesters who swarmed the premier's car as he attempted to leave a town hall event in the southwest town of Bunbury.
Mr McGowan has insisted he won't be deterred from getting as many people vaccinated as possible.
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