The Supreme Court on Monday blocked Arizona from enforcing a ban on most abortions after 20 weeks of pregnancy, in the latest blow for states that have tried to enact strict abortion laws.

The high court declined to hear an appeal from Arizona, leaving in place a prior ruling from the 9th U.S. Circuit Court of Appeals that determined the law was unconstitutional. The Supreme Court decision effectively strikes down the law.

Gov. Jan Brewer signed the ban into law in April 2012. Nine other states have enacted similar bans starting at 20 weeks or even earlier.

But several of those bans had previously been placed on hold or struck down by other courts. The latest Supreme Court decision could further embolden opponents of those laws.

In its ruling, the federal appeals court said the law violates a woman's constitutionally protected right to terminate a pregnancy before a fetus is able to survive outside the womb. "Viability" of a fetus is generally considered to start at 24 weeks. Normal pregnancies run about 40 weeks.

The 9th U.S. Circuit Court of Appeals said last year such bans violate a long string of Supreme Court rulings starting with the seminal Roe v. Wade decision in 1973.

But supporters of the legislation said the law was meant to protect the mother's health and prevent fetuses from feeling pain.

U.S. District Judge James Teilborg originally ruled it was constitutional, partly because of those concerns, but the 9th Circuit blocked the ban.

Lawyers representing Arizona argued that the ban wasn't technically a law but rather a medical regulation because it allowed for doctors to perform abortions in medical emergencies.

The Associated Press contributed to this report.