Bankers and policymakers are considering changing the way foreign-exchange benchmarks are calculated, or pushing clients to ditch benchmark-based trades, in response to global investigations into whether this vast market is rigged.

The topic was raised at a four-hour meeting in late October at the European Central Bank. Regulators in the UK, US, Switzerland, Hong Kong and elsewhere started looking into possible efforts to manipulate the $5.3 trillion-a-day currencies market earlier this year. Changes to the so-called fix are "top of the list in industry discussions," said one person who attended the meeting.