U.S. equities fell on Thursday, pulling back from record highs, on worries that a corporate tax cut could be delayed.

A proposed plan by Senate Republicans would push slashing the corporate tax rate from 35 percent to 20 percent until 2019. The move contrasts with a bill working its way through the House. The proposed Senate measure would also alter the individual tax system.

"That's what gave us this new leg down," said Art Cashin, director of floor operations at UBS, on CNBC's "Squawk Alley."

Expectations for tax reform have increased recently, helping lift the stock market to all-time highs. The major indexes briefly fell more than 1 percent on Thursday, but managed to close well off their session lows.

The Dow Jones industrial average finished 101.42 points lower at 23,461.94, with McDonald's as the biggest decliner; it fell 1.8 percent. The Dow briefly fell more than 250 points.

The pulled back 0.4 percent to 2,584.62, with industrials as the leading decliner; the sector fell 1.3 percent.

The Nasdaq composite lagged, falling 0.6 percent to 6,750.05.

The Russell 2000, which tracks small-cap stocks, fell nearly 0.5 percent. Companies in the Russell 2000 have more to gain from an immediate domestic tax cut since they are more likely to be U.S.-based and not sprawling global entities.