Steven Shrank, HSI agent in charge of the raid:

“This was not a immigration operation where agents went into the premises, rounded up folks, and put them on buses. This has been a multi-month criminal investigation where we have developed evidence and conducted interviews, gathered documents and presented that evidence to the court in order to obtain a judicial search warrant.”

I like that when justifying the raid, the agent in charge of the raid tacitly admitted they do regularly just burst onto a premise and round up people for buses.

It's worth pointing out that the people behind this raid are not recently appointed hacks - and that this was not at the direct mandate of the current administration. What is actually happening here is the entire agency is staffed with attack dogs who act without impunity or shame. And the only difference is that they feel emboldened to act, and whoever was in charge of oversight to hold them back is no longer there.

Even if there was some technical immigration violation here its not like any of the people involved were some sort of flight risk or criminal masterminds.

They could have simply notified the company and the people about a potential problem with their visas/paperwork and asked them to provide documentation otherwise or if their visas were expired/improper to return to Korea and apply for a new visa.

I think it makes sense since this was a techincal violation where they improperly used the Visa Waiver Program instead of applying for B-1 visas. They almost certainly would have received as employees of a South Korean chaebol—highly reputable, well-documented employers that consular officers typically view as strong B-1 cases for short-term business travel. South Koreans vigorously compete to work at these corporations and while 1 or 2 migth have been denied. It’s highly doubtful that a US consular officer would view them as a flight risk.

This September 4 raid happened 12 days ago. It has been in the news daily. It has its own Wikipedia article. But I haven't found any source that would clearly tell whether the workers had valid and legal work visas or not and/or if they in their situation would have needed such.