Credit unions have been attempting to counter that argument, saying that the tax exemption is vital to the industry.

Brady is keeping his plan under wraps and even some members of the Ways and Means Committee haven't seen the bill. And the bill may be a moving target, with changes being made in the final days before it is unveiled.

House and Senate GOP leaders as well as Trump Administration officials earlier this year outlined the framework for tax reform. While the outline specified some of the tax cuts to be proposed, it was not specific about how to pay for the tax cuts.

Deficit hawks on and off Capitol Hill are pushing Republican leaders to attempt to make the tax cuts deficit-neutral. In other words, for every dollar in taxes that is cut, another dollar in spending cuts or revenue increases would have to be found.

For instance, Robert Bixby, executive director of the Concord Coalition, said last week that Republican willingness to cut taxes without offsetting the cost of the tax is "risky business and deeply disappointing."

"While justified by some as a way to grow the economy, the long-term effect of deficit-financed tax cuts would likely be to slow economic growth and make a bad long-term fiscal outlook even worse," Bixby said.

And deficit hawks have been trying to counter Republican arguments that tax cuts will pay for themselves through increased economic growth.

Some members of Congress may try to cut so-called tax expenditures as a way to soften the impact the tax cuts would have on the deficit.

The blueprint outlined by the GOP leaders and the administration simply states, "Special tax regimes exist to govern the tax treatment of certain industries and sectors. The framework will modernize these rules to ensure that the tax code better reflects economic reality and that such rules provide little opportunity for tax avoidance."

In theory, that could mean that could include the credit union tax exemption for cuts.

The Trump Administration's FY2018 budget estimates the 10-year cost of the credit union tax exemption at $35.31 billion—a small amount compared with many other tax expenditures.

The congressional Joint Committee on Taxation estimates the credit union tax exemption will cost $14.4 billion between 2016 and 2020.

As a comparison, the Joint Tax Committee estimates that eliminating the deduction for charitable contributions, other than for education and health, would save $230.5 billion during the next five years.

During the past two years, several members of Congress have told credit union trade group conferences that they will fight to retain the credit union tax exemption.

In any event, Brady's unveiling of the tax plan is only the first step in the complex legislative process. The Ways and Means Committee has scheduled a markup of the plan for next week. At that time, committee members will be able to offer amendments to the package.

House Republican leaders are likely to limit the type and number of amendments that can be offered on the House floor.

The Senate Finance Committee will consider its own package of tax cuts. However, when a tax cut bill reaches the Senate floor, it will be protected from a filibuster by budget reconciliation rules. That means the legislation could pass the Senate with 51 votes, rather than the 60 votes that are often needed to pass legislation in the Senate.

The House and Senate will then reconcile their two bills and a conference report would then go to the floor and if it passes, to President Trump for his signature.