In the discussion trying to prove whether the language of "don't eat" in the torah, automatically includes the prohibition to benefit, the gemara tries to prove the point from sheratzim which are permitted to receive benefit from even though it says לא יאכל (yei'achel) which is a question even on Chizkiya. The gemara answers that although the language of "yei'achel" implies an issur hana'ah, the Torah writes לכם to imply that שלכם יהא, and permit benefiting from it. To which the gemara asks, if so it should permitted to benefit from it even lichatchila, why does the braisa say that one cannot be in the business of buying and selling non-kosher animals. The gemara responds that the pasuk also says יהיו - בהוייתן יהא. The Taz in Y.D. 117:16 points out that the contradiction in the pesukim that forbids selling lichatchila, but if it comes your way you can sell it and receive benefit, is the source that one is not allowed to buy and sell prohibited foods. The gemara implies that the prohibition to do business with forbidden foods is d'oraysa, because it is derived from the contradiction in the pesukim שלכם implying its permitted and יהיו implying that its forbidden. The compromise is that it is not an issur hana'ah but an issur to do business with forbidden foods (unless one just happens to end up with it).
Tosafos d.h. amar, says explicitly that it is an issur d'oraysa. However, Tosafos limits the issur d'oraysa to include only selling items that are eatable. One can process soaps and lotions from non-kosher animals.
The Rashba (cited in Taz) disagrees and holds that the nature of this issur is only d'rabonon due to a concern that one may come to eat from it. The gemara strongly supports Tosafos against the Rashba.