Treasury Secretary Steven Mnuchin said it's "not fair" to ask for the release of President Trump's tax returns to prove whether his newly released tax plan would benefit him.

"How are Americans going to know whether or not the president gets this benefit if he doesn't release his tax returns?" asked ABC's "This Week" host George Stephanopoulos on Sunday.

"George, that's just not fair because ... we haven't published the rules as to what is going to apply to the pass-through rates, so you're making certain assumptions that I don't think are correct," said Mnuchin in response to the question.

The pass-through rate refers to the tax rate corporations pay, which under the newly released GOP has been criticized for being lower than expected for a plan aimed at saving households more money.

"I wouldn't need to make the assumptions if we had the president's tax returns," Stephanopoulos responded.

ABC News reported President Trump would save $75.7 million under the GOP tax reform plan, which was based on the president's most recent financial disclosure form.

Stephanopoulos said "the president himself has said publicly that he is not going to get a benefit" from the plan.

Mnuchin said the "American people will be comfortable with the information they have," but conceded that the "pass-through rate is something we need to be careful about."

He added the administration plans to engage in full transparency as it develops the rules for implementing the tax reform that will ensure "that rich people can't take advantage of it."