It has also suffered from the cost of integrating True North Communications, which it acquired last year.
Interpublic's revenue for the quarter ending September 30 fell to £1.1bn from £1.2bn the same period last year.
The company, which owns advertising giants McCann-Erickson and the Lowe Group, along with the world's biggest PR network Weber Shandwick Worldwide, suffered most in its US operations, which recorded a decline in revenue of 15.7%, down to £624.7m. However, its overseas revenue grew by 6% to £489.4m.
John Dooner, chairman and CEO of Interpublic, said, "Given the uncertain political and economic environment, clients are understandably cautious and Interpublic's revenue performance reflects their concerns."
He said the company would focus on winning new business and controlling spending. In the third quarter, Interpublic implemented a cost-cutting programme announced earlier in the year.
Shares in Interpublic, listed on the New York Stock Exchange, closed up by 3.7% yesterday at $24.25 -- partly buoyed by an overall jump in the markets.
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