A total of 71 listed firms in South Korea received "adverse" audit opinions in 2020, up from 65 the year prior, as the COVID-19 pandemic increased business uncertainties, government data showed Tuesday.

An "adverse" opinion suggests that a company may have violated accounting standards or significantly misstated their financial records.

According to a survey of 2,293 listed firms by the Financial Supervisory Service (FSS), 97 percent of the firms received clean opinions in their audit results.

The 71 firms were given "adverse" opinions due to violations of accounting standards, insufficient cooperation from management or uncertainties over business perspectives, the FSS said.

The nation's top four accounting firms -- Samil PwC, Samjong KPMG, Deloitte Anjin and EY Hanyoung -- accounted for 31 percent of the auditor market share in 2020.

The four accounting firms' combined market share dropped from 38.2 percent in 2019 and 43.7 percent in 2018, the FSS said. (Yonhap)