Police said Monday they have booked 23 members of a major umbrella labor group for holding a massive rally in downtown Seoul in defiance of antivirus rules, which has sparked concerns over further infections amid rising new cases.

The Seoul Metropolitan Police said a special investigation team has launched a probe into 25 members of the Korean Confederation of Trade Unions (KCTU) over their role in holding the rally on July 3 and booked 23 of them for allegedly violating quarantine regulations.

Around 8,000 members of the KCTU participated in the rally to demand a revision to the labor act, despite authorities' repeated calls to cancel it amid the pandemic.

Most of the demonstrators wore masks but stayed close to one another during the rally.

So far, at least three protesters who attended the street rally have tested positive, while all attendants are required to take coronavirus tests under an administrative order issued by the Korea Disease Control and Prevention Agency (KDCA).

The police probe came as the nation is gripped by the fourth wave of the pandemic with a sharp hike in new cases in the Seoul metropolitan area, prompting authorities to raise the virus restrictions there to the highest level last week.

On Monday, the country added 1,252 COVID-19 cases, raising the total caseload to 179,203, according to KDCA.

In August last year, the country was hit by the second wave of the pandemic in connection with a church in northern Seoul and a massive anti-government rally. COVID-19 cases traced to the Aug. 15 rally reached 650.

Yang Kyung-soo, president of the KCTU, slammed the government for shifting blame for its failed COVID-19 response.

"The health authorities described the KCTU rally participant (infected with COVID-19) as a patient traced to an office in Gangseo Ward, indicating that the infection was not confirmed to be traced to the rally," Yang said in a statement posted to social media. "However, the prime minister took the lead and described the person as a KCTU rally participant, shifting responsibility for the failed antivirus effort to the KCTU."

Yang said the KCTU has asked all participants to take COVID-19 tests in order to relieve any concern despite questions about the effectiveness and logic of conducting mass tests after the virus' maximum incubation period of two weeks.

He reaffirmed the KCTU's plan to stage a general strike involving all 1.1 million members on Oct. 20.

"Let us fight by striking to change the fundamental structure of our society and defend workers' jobs and rights at this turning point," he said. (Yonhap)