Retail traders who drove record gains in South Korean stocks during the darkest days of the pandemic have been bracing for a new threat — the return of institutional players betting on share-price declines.

The world’s longest ban on short-selling stocks came to an end Monday, with stocks fluctuating between gains and losses. Nevertheless, the end of the ban has individual investors scrambling for strategies to protect their portfolios.

Some have cashed out large chunks of their holdings over recent weeks, while others are toying with the idea of trying short selling themselves. One influential group, the Korea Stockholders Alliance, even vowed to gather day traders into a force to fight short sellers — much the same way their U.S. peers took on Wall Street over GameStop Corp. — if equities begin to tumble.