Do I need invitation letter from Authorized Unit?

I am expat member appointed Bangladesh company from Sri Lanka, working as Merchandising Manager with a valid work permit issued by the Govt. of peoples’ republic of Bangladesh. i intend to visit China by the end of this month (tentative date: November 30, 2015) to attend the ‘Canton Fair’ on behalf of the company. I have visited PRC previously several times for business purpose with his passport.

Considering above, please advise, Do I need invitation letter from Authorized Unit of PRC or Invitation letter from my supplier is enough.