Four members of the Finks bikie gang and a female associate have been charged with alleged kidnapping, sexual assault and assault of a man in Sydney's west.

The incident is alleged to have occurred at a hotel in Vineyard in December last year.

Police will allege the victim was assaulted physically and with a weapon, was stabbed in the knee and burnt with boiling water over a period of about 12 hours.

He also sustained fractures to his skull and cheek bones and lost hearing in one ear.

Police were called after cleaners noticed blood spattered on the walls and furnishings.

The men, aged 22, 24, 35 and 49, were refused bail and are facing several charges including kidnapping, extortion, serious assault, malicious wounding and sexual assault.

A 30-year-old woman charged with demanding property in company with menaces with intent to steal, knowingly dealing with proceeds of crime and contributing to criminal activity was granted conditional bail.

The victim had been invited to the hotel and knew the people who allegedly assaulted him.

Police allege the man was burnt with boiling water to remove his bikie tattoo.

"[This] is quite consistent with outlaw motorcycle club culture," Detective Superintendent Deb Wallace said.

"When you leave a club... you must remove all identifiers that you have been a member of that outlaw motorcycle gang and if you don't remove it, they will remove it by force.

"We'll be alleging the victim was planning to leave the motorcycle gang or they didn't want him in the gang."

Strike Force Raptor detectives searched five homes in Hassell Grove, Kellyville, Rouse Hill and Schofield at 6:00am, arresting the five people.

Police expect more people will be arrested in relation to this incident.