Hong Kong’s securities regulator appears to be stepping up efforts to regulate cryptocurrency exchanges involved with initial coin offerings (ICOs).

In a statement released Friday, Hong Kong’s Securities and Futures Commission (SFC) revealed it has sent warning letters to seven cryptocurrency exchanges advising that certain tokens being traded on their platforms may be defined as securities. Though the names of the exchanges were not disclosed, the SFC indicated they are either based in or connected to Hong Kong, and among the top 20 in volume globally.

According to the note, the move is part of a wider effort by the SFC to caution investors about the risks of trading cryptocurrencies, one that began more mildly with a warning on the possible risks of the ICO fundraising model on Sept. 5 of last year.

Notably, the SFC said that the inquiry may result in further action, but that so far the exchanges notified all responded to the inquiry.