Ethics of a journal requiring that submissions cite existing articles in the journal
There are no explicit regulations regarding impact factors; the definition is too simple. (In terms of complexity, it's a lot like calculating a slugging average in baseball. So it's open to a lot of manipulation, and all of it is permissible. However, permissible does not mean ethical, and this is clearly a situation where, if true, the journal editors are trying to manipulate statistics to make their journal look better. Such a policy, if done with the intent of manipulating statistics, is deplorable, and should be denounced—via web campaigns, blog posts, open letters, and so on.

That said, there is a counterargument that is less nefarious in aim. It is possible to argue that you should, in general, cite some article from the journal you're submitting a paper to. If you can't do that, why is your article suitable for submission to that journal (let's call it journal X)? Presumably, there are a number of other journals (A, B, C, etc.) whose works you have cited instead of X. In that case, the journal could argue that your paper is a better fit for journals A, B, and C instead.

Since it's not clear for which reason the journal has the self-citing policy, I would make sure that you can determine it convincingly, one way or the other, to avoid embarrassing yourself. The last thing you want to do is spearhead a campaign that turns a molehill into a mountain.