The verse explains why the Levi and Kohen aren't given their share if they help out (Malachi 2:8). But why are the poor punished?
My notes say to look in Ohel Moshe
Barry Epstein, Dallas, USA
The reason they are punished is clear, being that Ma'aser Ani is supposed to be a gift and not any type of sale or wage. The Pesukim brought by the Beraisa merely are sources for this occurence regarding Kohanim and Levi'im, in addition to the severity of the matter for Kohanim and Levi'im (see Tosfos DH "v'Chi" that the Gemara doesn't really mean that they get put to death). However, it is clearly wrong for Ani'im to do so as well.
All the best,