A controversial abortion bill is on Gov. Haslam's desk, and it's unclear when or whether he will sign it.

The law would require a doctor to test for the viability and gestational age of a fetus.

It would ban abortions after 20 weeks -- that's five months -- unless the pregnancy was seriously threatening the woman's health.

A doctor violating this law could face a Class C felony, which carries a penalty of up to 15 years in prison.

Early last month, Tennessee Attorney General Herbert Slatery's office called the bill "constitutionally suspect, particularly with respect to the proposed post-viability abortion ban and the viability testing requirement."

RELATED: Tennessee AG: abortion ban bill 'constitutionally suspect'

Later, however, after lawmakers amended the bill to make it less subjective, Slatery said he would defend it in court, if it becomes law.

RELATED: Tennessee AG to defend abortion bill if it becomes law

Harlow Sumerford is Slatery's director of communications. He responded to WBIR's request for an update Monday about progress on determining the bill's constitutionality.

"The statute might not necessarily be immune to legal challenges," Sumerford wrote. "However, the law to some degree is unsettled, and we would be prepared to defend it.”

As Gov. Bill Haslam seeks input from attorneys on whether to sign this bill, WBIR 10News decided to Verify: is this abortion bill constitutional?

10News reached out to Gov. Haslam's office Monday. His press secretary Jennifer Donnals responded to our request, confirming the governor has not yet acted on this bill.

We also went straight to the text of the proposed legislation, Senate Bill 1180, which its authors are calling the “Tennessee Infants Protection Act.”

The bill's summary can be found HERE, and the full text is HERE.

10News sat down with Stewart Harris. He's a professor of constitutional law at Lincoln Memorial University's Duncan School of Law.

"There are a lot of different opinions - medical, scientific, religious, moral - on exactly when human life begins, and I'm not going to attempt to answer that question today," Harris said.

He - and 10News, for that matter - are simply discussing the constitutionality of the bill sitting on Governor Haslam's desk.

"This is going to be one of those issues that people feel passionately about on both sides," Harris said.

Haslam is trying to determine the law's constitutionality, too.

"In this one there are some questions around it," Haslam told reporters on Friday, "so I will have some conversations with my counsel and the attorney general."

Donnals confirmed Monday that is still the case.

Harris said one question centers on something called "viability."

In 1973, the US Supreme Court decision Roe v. Wade guaranteed a woman's right to an abortion in the first trimester.

Then, in 1992, the decision Planned Parenthood v. Casey changed that somewhat, saying whether a woman has a guaranteed right to an abortion comes down to "viability," that a woman has a right to abort the fetus pre-viability.

"Generally speaking, it's the ability of the fetus to live - to survive - outside the womb," Harris said. "The moment the fetus becomes viable, everything shifts, and the woman no longer has a right to an abortion. Indeed, the state now has the power to regulate abortion, even out of existence after viability, as long as it leaves an opening for the life or the health of the mother."

The bill on Haslam's desk says, "'Viable' and 'viability' mean that stage of fetal development when the unborn child is capable of sustained survival outside of the womb, with or without medical assistance."

"But viability has never been defined. When exactly is a fetus viable?" Harris said. "Going all the way back to Roe v. Wade, the Court noted that this was a moving target, that as technology advances, earlier and earlier pregnancies will provide viable fetuses."

The bill would call a fetus viable, unless otherwise certified by a doctor, at 20 weeks. That's five months.

"So it's pushing back what most people consider to be the dividing line between when a woman has a right to an abortion and when she doesn't," Harris said.

The bill also says doctors can face criminal charges if they fail to follow procedures.

"Even if they fail to fill in the paperwork properly, that's a misdemeanor," Harris explained, adding the bill "places all sorts of requirements on physicians as they try to determine whether something is viable or not."

So is Tennessee's proposed 20-week abortion ban legislation constitutional?

Harris says it's unclear.

"It's very much on the edge of what's constitutional," he said. "This is a very carefully crafted law. You can tell the people have read the Roe decision and the Casey decision - other abortion decisions, and they're using language that suggests that they're trying to work within constitutional limits, but what they're doing is they're pushing at those limits."

A number of other states have passed similar laws. Some of them have been struck down in the courts.

If Gov. Haslam signs this law, one thing is clear: it will likely face long battles in the court system.