According to St. Alphonsus Liguori, patron of moralists (in the same way St. Thomas Aquinas is the patron of theologians), yes.
In his Theologia Moralis, book III, paragraph 49, dealing with the definition of simony, he says:
"Simony is the eager will to buy or sell for a temporal price anything spiritual or spiritually annexed. (St. Thomas and others)… By 'spiritual' is meant anything supernatural directed to salvation, whether formally like the grace and gifts of the Holy Spirit, or causally, like […] prayers… From this it is evident that the wickedness of simony consists of the irreverence that is committed when spiritual things are judged according to a temporal price, and are subject to a contract, and it is by nature a mortal sin, and cannot be made venial by the levity of matter, since no gift of grace, no matter how small, can be sold without grave irreverence…"