Police looking into alleged illegalities during an overnight street rally in central Seoul last month raided an office of a construction labor union affiliated with the umbrella Korean Confederation of Trade Unions(KCTU) on Friday.

The Namdaemun Police Station sent investigators to the office of the Korean Construction Workers' Union(KCWU) in Yeongdeungpo District in Seoul at around 8 a.m. to secure materials and documents related to the rally.

Police inspectors confiscated desktops and laptops used by KCWU head Jang Ok-ki and other officials, as well as notebooks.

The police are looking into possible illegal acts during the protest on May 16 and 17 in central Seoul, with 29 people booked for violating the Assembly and Demonstration Act. 

Police have summoned Jang and another KCWU official for questioning four times, but they refused to appear, saying that they will not comply until after the funeral for a union member who died by self-immolation on May 1.