If you own a large advertising platform, and you have a stake in another company, are you than allowed to place an ad at a favorable place on that platform, a p

If you own a large advertising platform, and you have a stake in another company, are you than allowed to place an ad at a favorable place on that platform, a place so favorable it trumps any other content and even user’s ad-blockers? I’m not a lawyer, but there is something here that doesn’t smell right.