There’ve been numerous newspaper articles and government warnings about it, and a few scattered reports on this website of foreigners who got caught up in a raid or narrowly escaped. For example this article:
english.taipei.gov.tw/TCG/index. … newsid=550
There’s many other discussions on the topic of the legality of teaching English to under 6 year old students in the legal forums, though they are scattered about. There’s a lot of good info in this thread including references to the laws cited in the newspaper articles:
[Work rights for foreign spouses with a JFRV ARC
That said, despite the law, the crackdowns and all the warnings, there is still a very high demand from parents for english-only kindergartens. There’s plenty of them all over that are fairly openly doing this and just hoping their guanxi is good enough not to get shutdown. While the teachers don’t seem to get fined, they can have their work permit revoked and be ordered to leave the country.