Welcome to Tax Watch, a new feature focused on the fight over tax reform and the push to extend the 2017 Trump tax cuts this year.

House Budget Committee Chair Jodey Arrington (R-Texas) is worried that Republicans’ preferred accounting assumption for projecting the cost of their tax cut and spending bill could violate Senate rules.

Specifically, he’s concerned that it could break the Byrd Rule, which requires that bills have a material effect on the budget in the short term but no long-term effect. Arrington said that both of those requirements might not be met if Republicans use the “current policy baseline,” which bakes in the $4 to $5 trillion cost of extending the Trump tax cuts.

“My concern with [the Senate parliamentarian] rendering a positive position on it is that according to the Byrd Rule, whatever policy you legislate has to have a material impact to the budget. ‘Current policy’ wouldn’t show an impact to the budget,” Arrington told The Hill on Tuesday.

“One of the other main tenants is [that] you can’t increase the deficit outside the 10-year window. Well, even though there’s no impact to the budget, there is an increase to the deficit outside the 10-year window,” he added.

— Tobias Burns