Advertising technology firm PointRoll has sent an email to its clients warning them that their rich media ads could be pulled without notice by Yahoo, reports MediaPost.

The email warned that Yahoo has unilaterally decided to stop publishing rich media ads on its pages. About 30 publishers, including Yahoo, had placed PointRoll's rich media ads at no additional cost to the advertiser under the logic that they gave them an advantage over sites that were not publishing such ads.

Recently, however, Yahoo has dropped this policy and will require additional placement for rich media ads. The free upgrade to rich media ads was part of a PointRoll program labeled "Included."

Yahoo has recently begun selling its own rich media ads at no additional cost, effectively mimicking PointRoll's program.

The portal giant has said it would honor all rich media ads through May 1, but some advertisers are already seeing ads disappear and being replaced with standard units.