WPP shares slip after Ford says it will take bids from other ad agencies

The Ford Mustang is displayed during the 17th Shanghai International Automobile Industry Exhibition in Shanghai.

Shares in the world's largest advertising firm, WPP, fell Monday after investors learned that one of its biggest clients is reviewing its marketing spend.

Ford Motor Company said Saturday that it is to take bids from a number of other firms for some of its advertising that is presently managed by WPP.

The decision comes hot on the heels of the departure of founder and chief executive, Sir Martin Sorrell, who left the firm last week after 33 years amid an allegation of personal misconduct.

In a statement provided to CNBC by Ford Britain, the automaker said WPP would now have to compete to retain some of its existing business.

"We are going to place some portions of our advertising business up for bids with other agencies, including WPP, beginning in the coming weeks. No decisions have been made," Ford Britain said.

"We value the talented and creative women and men at WPP. They are trusted partners and curators of the Ford brand," it added.

The website Statista has estimated that in 2016 Ford spent $2.3 billion on advertising spending in the United States alone.

By mid-morning Monday, shares in WPP had lost more than 2 percent in value on the London Stock Exchange.

According to Reuters, WPP staff were sent a memo on Friday revealing Ford's decision. "WPP will have an opportunity to compete with other firms to retain these portions of the business, and will remain Ford's agency of record in some other key areas," the memo reportedly said.

CNBC contacted WPP but had not received a reply at the time of publication.