ANZ and NAB have both confirmed they are among 17 banks and two international broking houses named in a class action relating to the alleged rigging of the bank bill swap rate (BBSW) and bank trading in the United States.

Key points: The BBSW is the rate that determines what banks charge to lend to each other

The BBSW is the rate that determines what banks charge to lend to each other Banks being sued also include Macquarie, Deutsche Bank, HSBC

Banks being sued also include Macquarie, Deutsche Bank, HSBC Source claims the lawsuit is speculative in nature

The complaint was launched by two US-based investment funds, Sonterra Capital Master Fund, several Frontpoint Financial Funds, and trader Richard Dennis, whose nickname is the "Prince of the Pit". The case has commenced in the United States District Court for the Southern District of New York.

"The action names a number of defendants, including NAB, and references the proceedings brought by the Australian Securities and Investments Commission (ASIC) in relation to BBSW," NAB said in a statement.

"As we have stated previously, NAB does not agree with the claims by ASIC in relation to BBSW."

ANZ said it would be "vigorously defending the US class action complaint".

"ANZ notes there has been no allegation by ASIC of collusion between it and other institutions," the bank said in a statement.

Macquarie, HSBC among those in class action

Among the Australian and international banks being sued are ANZ, NAB, Westpac, Macquarie, Deutsche Bank, HSBC, JP Morgan, and Citi according to court filings.

Westpac has flagged it has not been formally served with any proceedings, but said it was aware of the class action filed in New York.

Westpac said it denies the "allegations in this claim and, if served with the claim, will defend those allegations vigorously".

The court filings allege that the defendants broke the law from at least January 1, 2003.

In the documents, the banks and stockbrokers are accused of rigging the BBSW by "co-ordinating manipulative transactions" during the fixing window, the five-minute period during which the rate is set each day.

The defendants are also accused of manipulating the benchmark rate by "artificially increasing or decreasing the supply of prime bank bills" during the period when the BBSW was being set, of sharing information on their BBSW rate exposure and co-ordinating "manipulative trades to maximise their impact on BBSW rates".

The plaintiffs have also accused the stockbrokers, Tullett Prebon and ICAP, of actively participating "in the conspiracy by facilitating manipulative trading for the bank defendants".

One source with knowledge of the matter told the ABC that the lawsuit was speculative in nature and was based on ASIC's civil case against ANZ, NAB and Westpac for alleged manipulation of the BBSW.

The Commonwealth Bank is also expected to be included in ASIC's case, but the bank declined to comment publicly.

A source the ABC spoke to said the class action was "opportunistic".

ASIC has already accepted enforceable undertakings from UBS, BNP Paribas and the Royal Bank of Scotland in relation to the BBSW fixing scandal.

BBSW is the rate that determines what banks charge to lend to each other. For banks, small differences in the rate that is set can equal many millions of dollars in profits or losses.

For the average consumer, the BBSW is a benchmark rate on many corporate loans, and can affect business loans, mortgages and credit cards.

ASIC in June said it would take three of Australia's major banks - NAB, ANZ and Westpac - to the Federal Court over the alleged rigging, with the corporate regulator describing some of the banks as being involved in "unconscionable conduct and market manipulation".