Story highlights Republicans can only lose two senators and still pass their tax plan in the Senate

Johnson cited concerns with the way the Senate's bill treats pass-through entities

(CNN) Sen. Ron Johnson announced he is opposed to the tax bill Wednesday, making him the first member of the GOP to formally come out against the party's plan, though the Wisconsin Republican said he was hopeful about being able to support a final version once changes are made.

Johnson issued a statement saying the current proposal in both chambers is imbalanced in favor of large corporations but he left open the door to supporting the bills if they are altered.

"Unfortunately, neither the House nor Senate bill provide fair treatment, so I do not support either in their current versions," he said. "I do, however, look forward to working with my colleagues to address the disparity so I can support the final version."

Johnson also told The Wall Street Journal that he is not able to vote for the bill as it's currently written.

"If they can pass it without me, let them," Johnson told the WSJ. "I'm not going to vote for this tax package."

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