The row is understood to centre around price, with the advertiser believed to be challenging ITV over why its airtime is charged at a premium compared with other channels.
Colgate-Palmolive spent £5.8m on ITV between November 2001 and October 2002 according to Nielsen Media Research.
The stand-off follows reports that other advertisers, including Procter & Gamble, are considering reducing spend on ITV over fears that the proposed merger between Carlton and Granada will push up the cost of airtime on the channel.
Tomorrow is the deadline for comments on the merger to the Office of Fair Trading, which is considering the proposal.
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