By Steve Olafson

Oklahoma City (Reuters) - An Oklahoma judge has rejected as unconstitutional a state law that would have required women seeking an abortion to first view an ultrasound image and listen to a doctor's description of the fetus.

The Ultrasound Act was approved in 2010 when the Republican-controlled Oklahoma Senate overrode a veto issued by then-Gov. Brad Henry, a Democrat. The law was immediately blocked by a temporary injunction and never was enforced.

The ruling on Wednesday by Oklahoma County District Judge Bryan Dixon said the law violates the state constitution because it is a "special law" that treats abortion differently than other medical procedures.

The Center for Reproductive Rights challenged the law on behalf of Nova Health Systems and Dr. Larry Burns, two of three abortion providers in Oklahoma.

Seven states mandate an ultrasound before an abortion, though the exact requirements vary, according to the Guttmacher Institute. In an eighth state, Virginia, such a law goes into effect in July.

(Editing By Corrie MacLaggan and Paul Thomasch)