RALEIGH, N.C. -- Gov. Bev Perdue vetoed legislation on Sunday that would have paved the way for North Carolina to drill for natural gas through a water and chemical intensive process known as fracking. It is the Democratic governor’s third veto of major Republican-backed legislation — all in the past four days.

Perdue said in a statement that she did not think the legislation went far enough to protect the environment.

“I support energy policies that create jobs and lower costs for businesses and families,” Perdue said. “Our drinking water and the health and safety of North Carolina’s families are too important; we can’t put them in jeopardy by rushing to allow fracking without proper safeguards.

The veto of Senate Bill 820 requires the House and Senate to attempt an override with three-fifths majorities. In the Senate, that would mean at least 30 votes and in the House at least 72 if all the members participated. Neither side had reached those numbers in approving the legislation.

House Speaker Thom Tillis and Senate leader Phil Berger, in a joint statement, called the veto a “flip-flop.”

“The General Assembly incorporated many of the governor’s recommendations in a bipartisan plan to begin developing the regulatory framework for affordable, clean energy alternatives,” they said. “We are disappointed, but not surprised, that when decision time neared, she once again caved to her liberal base rather than support the promise of more jobs for our state.”

Environmental groups praised Perdue minutes after the veto became public.

“Gov. Perdue stood up for our drinking water today,” said Elizabeth Ouzts, Environment North Carolina state director. “She stood up for our air quality and our rural landscapes, and against this dangerous approach to fracking.”

Fracking draws controversy. While it has generated jobs and business in states with sizeable natural gas deposits, questions about the environmental risks remain. Fracking involves drilling down and then horizontally into natural gas deposits that are trapped in shale, and then pulverizing the rock with a mix of water and chemicals to free up the natural gas.

Republican leaders contend that allowing fracking could pave the way for more jobs, and less reliance on foreign energy supplies. Environmentalists, who have had a majority of Democrat lawmakers on their side, say fracking poses great harm to public and private water supplies and the state’s natural gas deposits do not justify the effort.

Three weeks ago, the U.S. Geological Survey produced an estimate of far less natural gas in the state than state geologists had previously thought existed. The federal estimate said the state has 1.7 trillion cubic feet of natural gas in the Deep River Basin, which covers 150 miles from Durham to the South Carolina border. If the estimate is accurate, the deposits amount to about 5.6 years of usage based on 2010 consumption in North Carolina.

A state study found that fracking could be done in an environmentally safe way, but only under tightly regulated conditions.

Rep. Mitch Gillespie, a McDowell County Republican who co-authored the legislation, said the bill met the conditions set out in that study. He said he thought he had Perdue’s backing after agreeing to include more money for staff to handle fracking matters, only to find she had several additional conditions.

Gillespie said he tried to meet two of those additional conditions in a subsequent bill, but others either cost too much or were not reasonable.

“It’s hard to deal with somebody if they are constantly changing their deals,” he said.

Perdue issued an executive order in May that outlined her approach to allowing fracking in an environmentally safe way that included input from health, environment and public safety officials. The state legislation put those decisions in the hands of a panel of 12 voting members that includes six with ties to mining or natural gas production.

She said in her statement that she is not opposed to fracking and she had sought additional changes to the legislation.

In recent days, Perdue has vetoed a $20.2 billion state budget bill, largely because she thinks it does not do enough for education, and legislation that severely weakens a law intended to make sure those given the death penalty did not receive it as a result of racial bias. Both of those bills are scheduled for veto override votes this week.