Five of those charges relate to recruiting five other people to commit criminal acts by hindering a police investigation.

One of those people is understood to be his son Chris, a former employee of the Health Services Union.

Outside Maroubra police station in Sydney's east, the head of the Fraud Squad, Superintendent Colin Dyson, said that Mr Williamson hindered the police when he and his son removed a bag of documents from the union's Pitt Street headquarters while police were executing a search warrant at the premises in May this year.

Mr Williamson is also facing separate charges of asking others to delete computer files from the union's offices.

He is also alleged to have encouraged others to destroy documents relating to American Express credit card statements.

Superintendent Dyson said that another 15 charges stemmed from Mr Williamson making false statements with the intent to mislead members of the union.

Mr Williamson is also alleged to have fabricated documents that were later presented to the internal union inquiry conducted by barrister Ian Temby, QC, and accountant Dennis Robertson.

"These are very serious charges" said Superintendent Dyson, adding that they attracted a maximum penalty of seven years' jail.

Police said that further arrests were likely and that Strike Force Carnarvon's broader investigation into widespread allegations of corruption within the union were continuing.

Superintendent Dyson said that police now had "more persons of interest" than at the start of their inquiry in September last year.

Police said that bail would not be opposed but that they would ask for certain conditions to be met, including the surrender of Mr Williamson's passport.

Arrested this morning

Mr Williamson was arrested by appointment this morning.

The 59-year-old handed himself in at Maroubra police station at 7.45am today at the request of detectives from Strike Force Carnarvon.

At 9.10am Mr Williamson arrived at his two-storey house in Meagher Avenue, Maroubra.

Wearing a grey suit and a tie, he was seated in the back seat of a police car. About a dozen police officers arrived with him to execute a search warrant at the house.

Mr Williamson refused to answer any questions about the nature of his charges.

Before his arrival, his solicitor Vivian Evans arrived at the house accompanied by two other men.

Mr Williamson's daughter Alexandra, a former media adviser to Prime Minister Julia Gillard, had earlier told the Herald that her family would not be releasing any statements and would not provide any information as to her father's movements.

Suspended on full pay

Mr Williamson was the union's national president when he was suspended on full pay in September last year after a Herald investigation revealed that he had embezzled union funds.

It was also revealed that he and federal MP Craig Thomson, the union's former national secretary, received a secret commission in the way of an American Express card from a major supplier to the union.

In May this year police raided the HSUeast's headquarters in Pitt Street in Sydney's CBD.

While police were seizing documents and computer equipment upstairs, Mr Williamson and his son Chris were stopped with a black bag in a neighbouring underground car park.

While he did not name Mr Williamson, Detective Superintendent Col Dyson, commander of the fraud and cyber crime squad, later suggested that criminal charges might arise from "efforts [which] have been made to interfere with information relevant to our investigation".

But before police could inspect Mr Williamson's bag, his solicitor Vivian Evans lodged a claim of legal professional privilege over the contents. Communications between lawyers and their clients are confidential and not available to police.

The dispute over the contents of the bag was later resolved but it is still not known what Mr Williamson may have been trying to remove from the office while the police were executing their search warrant.

In July, the Temby report, an internal investigation into allegations of corruption within the union, found that nepotism and cronyism resulted in Mr Williamson, his family and friends reaping millions of dollars from the troubled HSU during his 15-year reign.

The report found that companies controlled by Mr Williamson and his family had received $5 million from the union over the past four years.

The report revealed that Canme, the company of Mr Williamson's wife, Julie, was paid $385,000 from 2005 to 2009. That amount is likely to be double as the Herald understands Canme was being paid up to $15,000 every two months from about 2000. Mr Temby raised questions as to whether the work was actually done.

Within days of the release of the Temby report, Mr Williamson handed in his resignation.

He had been collecting a salary of just under $400,000 a year form the union, and another $150,000 in union-related board positions.