JEFFERSON CITY, Mo. -- A federal judge on Friday blocked a new Missouri law that would have required a 24-hour waiting period for abortions.

The law, which had been scheduled to take effect today, requires physicians to wait a full day after consulting with women before performing abortions. A lawsuit by Planned Parenthood affiliates contends it is unconstitutionally vague.

Senior U.S. District Judge Scott O. Wright issued a temporary restraining order against the law and scheduled a Jan. 27 hearing on whether to impose an injunction.

He said Planned Parenthood had demonstrated a probability of success on its claims that the law fails to give abortion providers fair warning of what conduct is prohibited and that it encourages arbitrary enforcement of the law in violation of the constitutional protection of due process.

"If allowed to go into effect, the act presents plaintiffs with a choice: Continue to provide abortions under peril of criminal sanctions, or stop providing abortions," Wright wrote in his brief decision. "Each option entails irreparable injury to providers and/or their patients."

The legislature voted Sept. 11 to override Democratic Gov. Bob Holden's veto of the abortion bill, meaning it automatically would have become law 30 days later.

The law requires physicians to wait 24 hours to perform abortions after conferring with women about "the indicators and contra-indicators and risk factors, including any physical, psychological or situational factors." The so-called "informed consent" law allows violating physicians to be charged with misdemeanors punishable by up to one year in jail and a $1,000 fine.

Because of terms such as "situational factors," physicians would have been guessing as to how to fulfill the consultation requirements, the lawsuit said, and prosecutors could have come up with various interpretations when enforcing the law.

Wright held a private conference call Wednesday with attorneys for Planned Parenthood and Attorney General Jay Nixon's office, which is responsible for defending state laws. His office said then that the judge would issue a temporary restraining order Friday but did not provide any details as to the basis for the decision.

Anti-abortion advocates who supported the law have said they were not surprised by the restraining order and expect a legal battle that could last several years.

Twenty-one other states have some form of a one-day "informed consent" law in effect, and five others have laws currently under litigation or enjoined by courts, according to Americans United for Life.