Police have warned the public to be careful when dealing with $50 notes after thousands of fakes were seized in raids in Sydney and in the United States.

Three large commercial printing machines and more than 800 counterfeit $50 banknotes were found in police raids in Sydney's eastern and south-western suburbs on Wednesday (AEDT).

And at the same time, the US Secret Service seized more than 900 counterfeit Australian $50 notes in San Francisco and arrested a 36-year-old Australian.

Another 6000 counterfeit notes were found during a seven-month Australian Federal Police (AFP) investigation.

AFP Commander David Steward said people should be cautious when dealing with $50 notes because some fake money was still in circulation.

"I do want to just encourage people to take care when they're using ATMs, particularly, and they're coming across $50 notes."

The fake notes are softer, lighter and if you scratch your finger nail across the translucent window the star can be removed, he told reporters on Thursday.

In April this year, the Reserve Bank of Australia (RBA) discovered that a number of high quality counterfeit banknotes were circulating in Sydney.

It informed the federal police, who began investigating in conjunction with the NSW Police's Strike Force Raptor, which had been formed to investigate bikie gangs after a murder at Sydney airport.

Two men, aged 39 and 45, from Sylvania, in Sydney, have been charged with various offences under the Crimes (Currency) Act and are due to appear in court on Thursday.

The younger man will be in Sydney's Central Local Court while the older man is due to appear in Sutherland Local Court.

A 40-year-old Campsie man faced Burwood Local Court on Wednesday on charges related to counterfeit currency and was refused bail and remanded to December 6.

A 33-year-old Vaucluse man and a 37-year-old Caringbah man have been charged with offences related to counterfeit currency and given police bail.

Acting Chief Superintendent Mal Lanyon, director organised crime directorate, said the 45-year-old man from Sylvania had links to the Rebels outlaw motorcycle gang.

"This is probably the most obvious example where we've had evidence that (bikies have had) an involvement in there," Supt Lanyon said.

"Outlaw motorcycle gangs represent organised criminal groups, as a result they're very fluid and they're prepared to move across a range of criminal activity."

Police say drugs were also seized in the Sydney raids.

A 34-year-old Bondi man has been charged with attempted possession of three kilograms of cocaine and is due to appear at Central Local Court on Thursday.

The RBA says the fake banknotes are good quality but not perfect.

"The counterfeits that have been seized are a good quality reproduction of a banknote," it says in a statement on its website.

"However, they can be identified as counterfeits by checking the security features."