JEFFERSON CITY — Gov. Jay Nixon called reporters into his office last week to announce his administration had discovered a $4.8 billion mistake in the tax-cut bill the Legislature had adopted just a few days earlier.

Nixon’s administration argues that when fully implemented, the bill would exempt Missourians making more $9,000 in taxable income from the state income tax. Nixon cited a section in the bill that states when the phased-in tax reductions are fully implemented, “the bracket subject to the top rate of tax shall be eliminated.”

“This provision would cost $4.8 billion a year when fully implemented, wiping out 65 percent of the state’s general revenue budget, ultimately pushing Missouri into fiscal chaos,” Nixon said during his press conference. “It is hard to overstate the crippling impact this would have.”

The Nixon administration requested an opinion on the statutory language from Cheryl D. Block, a professor of law at Washington University in St. Louis. Based on more than 30 years of experience as a professor, Block concluded that under the new law those with incomes ranging from $8,000 to $9,000 would have to pay a 5.5-percent tax rate, while those with incomes of more than $9,000 would pay no tax at all.

Republican House and Senate leaders also conducted a press conference to voice their concerns with the governor’s interpretations of the bill.

“The Missouri House and Senate leadership, and the governing Republican majority caucuses in both chambers, completely stand behind and continue to support (the bill),” House Speaker Tim Jones, R-Eureka, said during the press conference.

“If this were a true, good-faith argument, Budget and Planning would have put this fiscal note at $4.8 billion,” said House Republican Leader John Diehl, R-St. Louis County. “They didn’t do that. They looked at it twice, they never discovered that. This is made up, and it’s made to distract from the real issues.”

The Republican leaders also cited that the governor had not once approached them regarding his issue with the language before it moved through both the House and Senate.

Nixon received the final draft on April 16, meaning that he has until Thursday to decide the fate of the bill.

This year, however, some of the Republicans who had voted to sustain the governor’s veto last year said they remained supportive of the current plan.