KakaoBank, the country’s mobile-only bank that went public a month ago, saw its shares fall for three consecutive days on Monday due to an expiring lock-in period for millions of its shares.

Shares in the banking arm of mobile giant Kakao declined more than 5 percent to 77,300 won ($66.76) in morning trade, while the benchmark Kospi inched up 0.04 percent.

Some 3.14 million shares or 8.72 percent of the total shares subscribed by institutional investors became available for trading as their lock-in period ended on Monday.

The downward pressure began when the market learned that the Korea Post sold 90 percent of its holdings in KakaoBank, pocketing more than 1.1 trillion won. Korea Post’s sell-off pushed down KakaoBank shares more than 7 percent on Wednesday.

“Korea Post’s block deal which followed that of Netmarble heightened market concerns over ample supply,” Choi Jung-uk, an analyst at Hana Financial Investment Co., wrote in a report on Monday. “Having said that, foreign investors are estimated to have taken more than 80 percent of the Korea Post block deal, an indicator of foreign investors’ interests in KakaoBank.”

Korea Post’s exit could instigate other early investors such as Yes24 to sell their shares, wrote Kim Soo-hyun, a researcher at Shinhan Financial Investment.

KakaoBank went public with the IPO price of 39,000 won per share and had the biggest market capitalization for a financial institution.