A controversial bill that imposes new state requirements on clinics that offer the abortion pill is likely headed for a constitutional challenge if passed and signed into law, as expected.

Opponents of the bill say it would force women seeking the abortion pill to undergo an invasive procedure known as a transvaginal ultrasound and would impose other restrictions that have been struck down by the federal courts.

Ken Falk, legal director of the American Civil Liberties Union of Indiana, said the legislation will be challenged in court “as soon as it’s signed into law by the governor.”

If so, it would be the second abortion-related bill passed by the Republican-controlled General Assembly over the last two years to be challenged in court. Last November, a federal appeals court barred Indiana from enforcing a 2011 state law that would have stripped Medicaid funding from any healthcare provider that offered abortion services. Falk brought that 2011 case against the state on behalf of Planned Parenthood of Indiana, which stood to lose funding for all healthcare services it provides because it also offers abortion services.

The current legislation, Senate Bill 371, which passed out of the Senate last week on a 33-16 vote, covers clinics that dispense an abortion-inducing drug, RU 486, which can only be used during the early weeks of pregnancy.

Women who receive the drug at the clinic would be required to have a ultrasound. The bill doesn’t specify what type of ultrasound must be done.

The bill’s author, Republican Sen. Travis Holdman, said he’s had several physicians tell him that a less invasive, abdominal ultrasound can be performed. But Falk points to the testimony of several medical experts, including Dr. John Stutsman, an Indiana University School of Medicine professor and obstetrician-gynecologist, who told legislators that the bill would essentially force women seeking the procedure to undergo an invasive transvaginal procedure because the abortion pill is given early on in pregnancy, when the embryo or fetus is too small to be detected by an abdominal ultrasound. In a transvaginal ultrasound, a several-inch long probe is inserted through the birth canal into a woman’s uterus.

Falk described it as a “grossly invasive procedure” that violates the standards that U.S. Supreme Court has set for how states can limit access to legal abortions.

The ultrasound issue is playing out in the courts. Several states now require women who have an abortion to have an ultrasound. But in two states, North Carolina and Oklahoma, the mandatory ultrasound laws have been challenged in court.

A federal court struck down the Oklahoma law, which would have required transvaginal ultrasounds in some cases, as “blatantly” unconstitutional. North Carolina’s law is on hold, after a federal court issued a temporary injunction.

But a federal appeals court has decided to let Texas’ mandatory ultrasound law remain on the books.

Last year, the Virginia legislature considered a bill that would mandate transvaginal ultrasounds for women having abortions, but pulled back after the state’s conservative Republican governor questioned whether the law was constitutional.

“The courts are split on the issue of mandating ultrasounds,” said Stephanie Toti, senior staff attorney with the Center for Reproductive Rights.

State Rep. Sharon Negele, a freshman Republican from Attica who’s sponsoring the bill in the House, said “it’s premature” to be talking about the whether the bill is constitutional.

“It’s still in the process,” Negele said. “We still have to debate in the House.”

But Falk’s concerns about the constitutionality of the bill in its current form are significant because of his track record: As head lawyer for the ACLU in Indiana, he’s successfully challenged a string of state laws that were popular with legislators but posed constitutional issues. They include legislation that would have allowed police to stop and arrest people they suspected were illegal immigrants and a law that prohibited registered sex offenders from using social networking sites such as Facebook.