Organtree denied wrongdoing and explained that its role was to give a platform for would-be donors to register their interest in having their organs used after they die.
It said in a statement: "These serious allegations are untrue and amount to scaremongering of the worst sort."
The statement adds: "It is acknowledged and accepted that offering a reward is illegal but receiving expenses associated with the death of a loved one is not.
"The HTA's interpretation of the prevailing law is different to ours but it does not make their view correct."
