Australia’s big banks are caught up in an international rate rigging trial that could cost them billions.

ANZ, NAB, Westpac, CBA and Macquarie are among a number of international banks hit with legal action this week.

Prosecutors in the US allege traders at the banks rigged the ‘bank bill swap rate’ (BBSW), which regulates loans between banks and helps them set rates for business and commercial loans.

Fudging the rate could create millions in profits for traders.

ANZ, Westpac and NAB have already denied the allegations, while the others are expected to fight the allegations too.

The complaint includes claims of racketeering, wire fraud and collusion under America's RICO act.

Court documents say there was a “reasonably foreseeable effect on United States' domestic commerce” in the alleged rigging.

Labor is using the case in its campaign against the banks.

“This blows a hole in the argument put by the banks that this was a victimless act. Customers and shareholders have been treated like mugs for too long,” Senator Sam Dastyari said.

“The banks not only face the potential of major fines – they now risk significant legal action."

“It is the reckless behaviour of the banks that has put them in this position. They might try to again blame a few rouge elements, but this goes all the way to the top.”

ANZ, Westpac and NAB are engaged in a legal stoush with ASIC over alleged rate manipulation.

The new US complaint was filed in the United States District Court for the Southern District of New York by Florida derivative trader Richard Dennis and hedge fund Sonterra Capital Master Fund and Frontpoint Financial Services.

If they succeed in their bid for a jury trial, it could deal a serious reputational blow for the banks that are already being slammed in Australia.

The US complaint says that the ASIC action revealed “rare ‘smoking gun’ evidence, including emails, phone calls, and electronic chats, demonstrating a conspiracy among BBSW panel banks and inter-dealer brokers to fix the prices of BBSW-based derivatives”.