Switzerland’s competition authority is imposing fines totalling nearly 90 million Swiss francs (CHF) – about US$91 million – on five banks for colluding to rig foreign exchange markets.

The biggest single fine, of CHF 28.5 million, was imposed on Citigroup, followed by Barclays (CHF 27m), RBS (CHF 22.5m), JP Morgan (CHF 9.5m) and Japan’s MUFG (CHF 1.5m).

The Swiss Competition Commission, aka Weko, found that traders at the five banks had worked together in a cartel-style arrangement to manipulate currency prices for their own gain.

Weko’s penalty came three weeks after the European Union (EU) fined the same five banks a total of €1.o7 billion after its own five-year investigation into manipulation of the $5trillion-a-day forex market.

In both cases UBS Group escaped a fine because it blew the whistle on the other banks’ misconduct, while Credit Suisse is reported to be contesting allegations that it also participated and has refused to settle.

The rigging of the rates involved traders exchanging information in online chat rooms between 2007 and 2013 in cartels they called the Three-Way Banana Split and Essex Express.

Since allegations of benchmark currency rate manipulation first surfaced in 2013 more than a dozen financial institutions have paid almost $12 billion in fines around the world.

UK banking watchdog the Financial Conduct Authority (FCA) held its own investigation into the affair and handed out fines of £1.3 billion in 2014 over regulation breaches, whereas the EU and Swiss authorities were investigating the impact on competition.