A leading European foreign exchange broker filed for administration on Monday and a Danish bank conceded it faced heavy losses as the UK’s market regulator stepped in to assess the damage wreaked on the industry by last week’s violent swing in the Swiss franc.

The Financial Conduct Authority sent letters to an unspecified number of currency brokers on Friday asking them to update the regulator about any impact the Swiss move could have had on their balance sheets, according to a person familiar with the situation.

Global markets were left reeling last Thursday when Switzerland unexpectedly abandoned its currency ceiling against the euro. In one of the most damaging currency swings in the modern trading era, the Swiss franc soared in value, leaving investment banks across the world with big losses and hitting foreign exchange brokers particularly hard.