Sponsor Adidas is ending its commercial agreement with the governing body of athletics three years early, despite the IAAF's plans to broadly reform itself in the wake of doping and corruption scandals.
An IAAF statement on Friday, on the eve of its special congress to approve reforms, said: "Our commercial relationship concludes at the end of 2016."
The original 11-year partnership agreement, which started in 2008, granted the German sports apparel manufacturer global sponsorship rights until 2019.
That was under former IAAF president Lamine Diack, who is facing corruption allegations in France after revelations of doping cover-ups involving athletes from Russia.
Sebastian Coe, who replaced Diack as IAAF president in August 2015, hopes to push through major changes to the way the IAAF handles doping cases and governs itself at the congress in Monaco on Saturday.
The IAAF said it would "shortly" announce a new replacement sponsor. It thanked Adidas for "its longstanding support of athletics and close partnership with the IAAF."
In its own statement, Adidas said the two sides mutually agreed to end their agreement: "We would like to thank the IAAF for a successful and professional cooperation."