In a somewhat surprising move given her staunch pro-life posture in the past, Oklahoma Republican Gov. Mary Fallin has vetoed a bill that would make it a felony for physicians to perform abortions. Had it become law, the measure would have effectively outlawed abortions in the Sooner State.

Gov. Fallin, who calls herself “the most pro-life governor in the nation” and is on Donald Trump’s short list for VP, says she is rejecting the bill because it is “vague and would not withstand a criminal constitutional legal challenge.”

SB 1522 would have made it a felony punishable by up to three years in prison for a physician to perform an abortion. State law already makes it illegal for anyone not a doctor to perform an abortion. The bill would exempt physicians who perform abortions to preserve the life of the mother.

Said Gov. Fallin in her statement announcing her decision, “The bill is so ambiguous and so vague that doctors cannot be certain what medical circumstances would be considered ‘necessary to preserve the life of the mother.'”

Still, Gov. Fallin had been expected to sign the bill. As The Hill notes, “She has never vetoed an anti-abortion bill as governor and stuck to her position during her time in Congress was well.” Signing the bill also would “cement her place among the GOP’s Christian right and position herself to land on Trump’s ticket.”

Her veto has already stirred up cries of betrayal. “As one who proclaims to be pro-life, her actions run counter to her words,” commented Mat Staver, Founder and Chairman of Liberty Counsel. “This is a despicable betrayal of her word and of innocent children whose lives will be cut short because of her cowardly act. I encourage the Oklahoma legislators to veto the governor and Liberty Counsel stands ready to defend this bill.”

The Oklahoma Legislature may override a veto by two-thirds vote of each house. The State Senate passed the bill Thursday with a vote of 33-12. It passed the Oklahoma House of Representatives by a vote of 59-9 in April.

The bill’s sponsor, Republican Sen. Nathan Dahm, has said the measure was aimed at ultimately overturning Roe v. Wade, the U.S. Supreme Court’s 1973 decision legalizing abortion nationwide.

Gov. Fallin said in her statement that her goal is to see Roe v. Wade overturned as well, but that she does not think this is the right bill to make it happen. “In fact,” she said, “the most direct path to a re-examination of the United States Supreme Court’s ruling in Roe v. Wade is the appointment of a conservative, pro-life justice to the United States Supreme Court.”

You can read Gov. Fallin’s full statement announcing her veto right here.