It is expected to be hit by a $1bn (£621m) fine, divided between four regulators across the UK, US and Switzerland.
That is more than double the £290m charge Barclays attracted earlier this year, and represents a major blow to a bank already reeling from a rogue trader scandal and in the process of laying off 10,000 staff to cut costs and exit underperforming businesses.
Libor, the key inter-bank lending rate, is used to determine how much interest is charged on hundreds of trillions of dollars worth of financial products across the world, but dozens of banks are believed to have entered false information into the process.
Barclays’ fine came with a wave of bad publicity, making other banks keen to avoid being the next in line. But UBS has lost that struggle, and is likely to be hit on Monday or Tuesday.
RBS is expected to follow soon after, with chief executive Stephen Hester last month explaining he wants to settle the claims before the bank’s results in February.
Three financiers were arrested earlier this week over Libor fiddling claims, thought to include former UBS trader Thomas Hayes.
UBS, the Financial Services Authority, the US Department of Justice and the Commodities and Futures Trading Commission all declined to comment.