Scaled back mortgage-interest deduction raises concerns

"It's not the way to go about it," Ellis said. 

Ellis argues that the fiscal panel's overall proposal actually raises net taxes by nearly $1 trillion over 10 years. 

Although the National Commission on Fiscal Responsibility and Reform proposes a realignment of tax brackets, that move wouldn't be enough to offset the tax increase of reducing the mortgage-interest deductions, Ellis said. 

Berman also expressed concern about proposals to tax dividends and capital gains at ordinary tax rates, which would "seriously impact investment in commercial real estate."

The panel would need 14 of 18 members to agree on a plan for it to receive an automatic vote from Congress, which looked doubtful on Wednesday.