I have seen brokers do this for certain stocks on the OTCB and pink sheets.

When there is a stock that they feel is acting funny/fishy...  they will reject any online orders and you have to call  it in.

I remember they did that with  CSHD  (a scam)  and NWOL (Formerly NDOL NWOG)

Not sure what would cause them to pick up red flags here....?