Standard & Poor's has cut Fairfax's credit rating, citing an ongoing deterioration in the company's advertising revenue and uncertainty about how it will recover earnings.
The ratings agency has lowered the media company's rating from triple B-minus to double B-plus.
Standard & Poor's says the downturn in advertising has gone beyond what it had factored in at this stage of the economic cycle.
The ABC reports shares in the publisher of The Sydney Morning Herald and The Age plunged more than 7% around 10.30am (AEST) on Thursday.
Fairfax says it will probably now face another $A10 million in interest charges this financial year, but says it is comfortably inside its debt obligations.