BUENOS AIRES—Argentina’s government imposed stricter capital controls to protect its foreign-currency reserves a day after voters returned the leftist Peronist movement to power in a defeat for pro-business President Mauricio Macri.

Central Bank President Guido Sandleris said Monday that the measure was necessary to staunch a depletion of reserves that accelerated last week amid a crisis of confidence that has led to financial-market volatility.

“We believed that there was the risk that this would continue this week,” Mr. Sandleris said. “This is a way to protect the reserves and to give the next administration more freedom while designing its economic policies.”

Individuals seeking to buy dollars will now have a limit of $200 a month, or $100 if the transaction is in cash. The previous limit, imposed in September, was $10,000 a month.

The stricter controls will likely increase demand for dollars on the black market, said Capital Economics, a London-based consulting firm. “Overall, this will weigh on real activity and offset any benefit of a more stable official currency on inflation,” it said.