Oklahoma Gov. Mary Fallin vetoed a sweeping and unprecedented measure Friday that would have made performing an abortion a felony punishable by prison time, saying the bill was vague and would not be able to withstand a criminal constitutional challenge.

The bill, part of an overt strategy to challenge the Roe v. Wade Supreme Court ruling, had passed the state senate 32-12 without debate and had gone to the governor's desk.

“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,’” Fallin, a Republican, said in a statement.

“The absence of any definition, analysis or medical standard renders this exception vague, indefinite and vulnerable to subjective interpretation and application,” she said.

Fallin is staunchly pro-life and has signed 18 bills supporting pro-life causes. Lawmakers can still attempt a veto override, which requires a two-thirds majority in each chamber.

Abortion-rights supporters said the measure was clearly unconstitutional, but the bill's author said he hoped it would be a first step toward overturning the 1973 Roe ruling that legalized abortion.

“Since I believe life begins at conception, it should be protected, and I believe it's a core function of state government to defend that life from the beginning of conception,” Republican Sen. Nathan Dahm, the bill’s author, said.

Under the bill, doctors who perform abortions would have faced three years behind bars and lose their medical licenses. There were no exceptions in the case of rape or incest but consideration would have been given if a mother’s life is in jeopardy.

Abortion rights supporters -- including the state’s medical association – argued the bill was unconstitutional and vowed to fight it.

State Sen. Ervin Yen, the only doctor in the Senate and a Republican, described the legislation as “insane” and voted against it.

The Center for Reproductive Rights also slammed the bill, describing it as “cruel and unconstitutional.”

The Associated Press contributed to this report.