The National Federation of Independent Business said Thursday it opposes the tax plan proposed by Republicans in the House of Representatives.
"This bill leaves too many small businesses behind," CEO Juanita Duggan said in a statement. "We are concerned that the pass-through provision does not help most small businesses. Small business is the engine of the economy. We believe that tax reform should provide substantial relief to all small businesses, so they can reinvest their money, grow, and create jobs."
Meanwhile, Todd McCracken, CEO of the National Small Business Association, said in a phone call with CNBC that he was still unsure whether his organization would support the bill.
The nonpartisan Small Business & Entrepreneurship Council said in a statement that it sees the legislation as an opportunity to modernize the tax code. The group said it supports certain provisions in the proposal, such as the repeal of the estate tax and its expensing provisions.
The group's chief economist, Ray Keating, noted that they are still reviewing some areas of the legislation where the organization has concerns.
The groups have all been pushing hard for tax reform.
The House bill, titled the Tax Cuts and Jobs Act, would slash the number of income tax brackets from seven to four: 12 percent, 25 percent, 35 percent and 39.6 percent.
The bill is also expected to raise the child tax credit to $1,600 from its current maximum of $1,000. It's also expected to preserve popular retirement savings plans, such as 401(k)s and Individual Retirement Accounts.
Business Roundtable said Thursday it would support the plan.
"If we are serious about growing the economy, creating jobs and increasing wages for all Americans, this country needs a modernized tax code. It is that simple," said Jamie Dimon, the chief executive of JP Morgan Chase and chairman of Business Roundtable.