Concerns over staffing and patient safety will be front of mind as nurses and midwives rally outside a western Sydney hospital.

The NSW Nurses and Midwives Association says around 35 nurses and midwives have quit Blacktown Hospital's emergency department since December, leaving more than 115 job vacancies across the entire hospital.

Nurses finishing their shift at 3.15pm on Tuesday will rally to draw attention to staff shortages, which they say leave them exhausted and grappling with unsafe workloads.

Nurses union assistant boss Michael Whaites says the issue is before the NSW Industrial Relations Commission.

"We have held serious concerns about unsafe staffing at Blacktown Hospital for an extended period," he said.

"A sad reality is these issues could largely be addressed by the NSW government listening to frontline nurses and midwives and introducing shift-by-shift safe-staffing ratios.

"It's causing widespread angst across the health workforce the longer this government and bureaucrats continue to ignore the issues."

The Western Sydney Local Health District has been contacted for comment.