Unity background thread logging

I’d like to implement some async logging for Unity, for that I need to post some JSON from a background thread. Unfortunately I get the following error message:

enforceWebSecurityRestrictions can only be called from the main thread.
Constructors and field initializers will be executed from the loading thread when loading a scene.
Don’t use this function in the constructor or field initializers, instead move initialization code to the Awake or Start function.
UnityEngine.WWW:.ctor(String, Byte, Dictionary`2)
WebLogger:Loop() (at Assets/Logging/WebLogger.cs:43)

I understand that I cannot modify 3D related objects from the background thread, but I am really surprised that I cannot even post WWW data. How should I approach the issue? How can I call a website without causing the main thread slowing down?

Thank you for your answer.

I started to post the data with WebClient instead of the rubbish WWW class. It works properly.