27 December 2006, President of Romania Mr Traian Basescu approved a new law for Religion, under it, Denomination with less than 20 thousand members cannot register legal status in the country. No big deal, spokesman in the country says, because 20K people is about 0.1% of the population only, and it is expendable. (Link)
Same theory applies here, they have to either migrate or force to go underground.
Update: Opinion from anonymous,
"They are not illegal, they just are not considered cults and don't receive some advantages from the state. They are not banned from worshipping, as the term illegal would imply. Nobody would chase members of this church and force them to convert. "
I appreciate this comment very much, and I also understand Media will always surely have their Agenda when reporting news. So, in order for the opinion to have value, it is better that it is not from some anonymous sources. However, I very much thank this other side of the story.