Senator Ron Johnson (R-WI) became the first Republican U.S. Senator to come out against the tax reform plan working it’s way through congress, even as the House of Representatives is prepared to pass their version of tax reform Thursday. Johnson told the Wall Street Journal that his opposition to the bill is because of the way small businesses are treated compared to large corporations.

“If they can pass it without me, let them,” Johnson said in an interview Wednesday with the Wall Street Journal. “I’m not going to vote for this tax package.”

From the Wall Street Journal:

The Senate bill would provide $1.3 trillion in gross tax rate cuts to corporations, according to the Joint Committee on Taxation. That compares with $362 billion in gross tax cuts for pass-through entities. Both types of businesses also would lose some tax breaks.

More companies are organized as pass-through businesses than as corporations. Many pass-through filers are small businesses. Overall U.S. business income is split roughly evenly between the pass-through businesses and corporate income.

“I have no problems in making all American businesses competitive globally,” Mr. Johnson said. “This isn’t anti-big corporation at all. When you’re going to do a tax reform, you have to treat them equitably so they can maintain their competitive position here at home as we’re making them competitive globally.”

Johnson also complained that small businesses that pass-through entities are expecting a rate cut similar to large corporations.

“That is still buffaloing people, pass-throughs that think they’re getting a 25% rate,” Johnson told the newspaper. “It’s still lost on a lot of people.”

However, Johnson could still change his vote, according to an interview he gave CNBC. “I want to get this thing fixed, and vote for pro-growth tax reform that makes all American businesses competitive globally,” he said in the interview. “I care deeply about this country, I care deeply about this deficit.”

Johnson added that he spoke with President Donald Trump about the issue. Johnson said Trump told him, “I will work my tail off over the weekend to fix this problem.”