The young Kiwi mother wanted by the FBI for kidnapping is now facing US court charges for cashing fake money orders.

A criminal complaint was filed last week against Bianca Ormsby, 21, who brought her baby daughter Sydney to New Zealand against the terms of a joint custody agreement with the father, Adam Thomas.

The complaint was filed in the United States District Court in Michigan by Special Agent Marc Miles from the United States Treasury Inspector General for Tax Administration.

An affidavit filed by Miles alleged four counterfeit US Postal Service money orders and a forged Treasury refund cheque, worth a total of about $7500, were deposited into Thomas' bank account last June.

His affidavit said his service received information last August about suspicious deposits into the account, from the Internal Revenue Service, the bank's fraud department and Thomas.

Thomas said he allowed Ormsby to use his ATM card to access money if needed for their daughter. He claimed she told him she was depositing cheques from her father.

ATM photographs captured a woman who appeared to be Ormsby depositing the bogus refund cheque, the affidavit said.

Ormsby has been wanted by the FBI since fleeing to New Zealand in March with Sydney, who was then 10 months old.

The New Zealand citizen has lived in the US with her family for several years.

She began dating Thomas while at college but they split a few months after Sydney was born. Thomas discovered Ormsby had secretly left the country after going to pick up the baby as arranged in March, and finding them gone.

New Zealand police have been liaising with US authorities but won't say whether they had been in contact with Ormsby.

FBI special agent Sandra Berchtold said the federal complaint was still active but refused to comment further.

Ormsby's father, Adrian, who lives in Michigan, questioned the new allegations, and referred to internet postings blaming Thomas for the fake cheques.

He said his daughter relied on family members for food and nappies because she had no access to money from Thomas.

Ormsby had received abusive emails, including hate mail and death threats, after media reports about her case, he said. She had even been subjected to obscenities from strangers while walking with Sydney to the shops.

Ormsby's supporters on Facebook site Bianca Sets the Record Straight were still backing her this week.

Postings said Ormsby was breastfeeding her 5-week old baby at the time of the alleged offences and couldn't have been behind the cheque scam.

Supporters said it was unlikely she would have deposited money into Thomas' account at a time when their relationship was fraught and he was refusing to spend money on his daughter.

New Zealand family members said Ormsby had asked them not to talk about her, and said she didn't want to speak to media.

Her lawyer was unaware of the new formal complaint, but said Ormsby knew authorities were looking into the matter. Thomas also said the development was "news to him", and he had been advised by lawyers not to comment.