Denmark's financial services regulator on Friday ordered Saxo Bank A/S to hand over details of its handling of Swiss franc trades amid chaotic moves in the currency earlier this month.

The brokerage is under fire from clients after it altered the prices on their Swiss franc trades hours after they thought they'd closed--magnifying many mom-and-pop traders' losses and leaving them hundreds of thousands of dollars in the red. The franc shakeout on Jan. 15 followed a shock decision from the country's central bank to abandon the limit on its value against the euro.

Finanstilsynet--the Danish financial regulator--said it has received a small number of complaints regarding the broker's handling of the situation on Jan. 15, and "is currently in close dialogue with Saxo Bank and will require the bank to provide a detailed report on the actions taken during and after the incident," it said in a statement.

Saxo Bank has said it is pursuing customers with negative balances, and is prepared to face lawsuits to recover its cash. "It's not unlikely that we'll face legal challenges, but that doesn't change the case from our side," Steen Blaafalk, group chief financial and risk officer, said earlier this week.

Write to Tommy Stubbington at tommy.stubbington@wsj.com

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