Vice presidential nominee Tim Kaine votes mostly with the Democratic party line — about 96 percent of the time, as GovTrack Insider reported in an article last week. But the Virginia Senator is now causing worry among many of the party faithful with his stance on abortion funding. It all relates to a provision known as the Hyde Amendment that bans federal taxpayer funds from being used for abortion.

What is the Hyde Amendment?

The Hyde Amendment was named after then-Rep. Henry Hyde (R-IL6), who introduced it shortly after the Supreme Court decided Roe v. Wade. It has been passed as a temporary measure by Congress every year since 1976, to ban federal taxpayers dollars from being used for abortion — except, since 1989, in the case of rape, incest, or if the life of the mother is at stake.

The amendment has been consistently renewed each year, when Congress was controlled either by Republicans or Democrats, and even during the Democratic-led crafting of the Affordable Care Act, popularly known as Obamacare.

Between the time abortion was made legal nationwide in the 1973 Supreme Court case Roe v. Wade to when the Hyde Amendment took effect in 1980, Medicaid paid for about 300,000 abortions per year. (Without federal funding, women may be paying out of pocket or turning elsewhere for help: 15 states currently allow state funds to be used for abortion.)

Supporters in the pro-life movement have two main reasons for supporting the Hyde Amendment: “Americans personally opposed to abortion do not want their tax dollars paying for the procedure, but more importantly, abortion funding restrictions save lives,” writes Americans United for Life staff counsel Mary E. Harned.

But opponents say that “Any right that requires you to take extraordinary measures to access it is no right at all … not as long as we have laws on the book like the Hyde Amendment making it harder for low-income women to exercise their full rights,” Hillary Clinton has said.

Kaine and Clinton have disagreed on the issue

Kaine’s voting record on abortion in the Senate has been almost uniformly pro-choice, with NARAL Pro-Choice America scoring him at 100 percent on the issue. But he has expressed his personal opposition to the practice due to his devout Catholic faith. Clinton, whose ticket Kaine is running on, is a Methodist, but has broken with her church’s doctrine opposing abortion.

Nowhere is that difference more apparent than regarding the Hyde Amendment, with Clinton calling for its repeal going back years. Kaine has voted in favor of the amendment in the past. This week several mixed messages were sent by Kaine and the Clinton campaign.

First, Clinton campaign staffers claimed that Kaine personally told Clinton that he has changed his view since joining the Clinton ticket and is now calling for repeal. However, many Democrats and progressives weren’t entirely convinced, since Kaine had expressed his support for the amendment as recently as last month. Then Kaine himself told CNN on Friday “I have not changed my position on that.” Then a campaign spokesperson told the Wall Street Journal that Kaine personally supports the Hyde Amendment but “is committed to carrying out Secretary Clinton’s agenda.”

For the first time, the official Democratic platform adopted at their national convention last week includes a provision advocating for repeal of the Hyde Amendment. The platform states:

“We believe unequivocally, like the majority of Americans, that every woman should have access to quality reproductive health care services, including safe and legal abortion — regardless of where she lives, how much money she makes, or how she is insured. We believe that reproductive health is core to women’s, men’s, and young people’s health and wellbeing… We will continue to oppose — and seek to overturn — federal and state laws and policies that impede a woman’s access to abortion, including by repealing the Hyde Amendment.”

Kaine’s vote on the Justice for Victims of Human Trafficking Act

The issue sparked controversy last year when a provision similar to the Hyde Amendment was added to a human trafficking bill that was otherwise expected to pass with large bipartisan majorities. The Justice for Victims of Human Trafficking Act, S. 178, eventually passed after a compromise was reached that created two separate funding streams for trafficking victims: one with federal dollars subject to the Hyde Amendment, the other with money collected from criminal offenders not subject to the amendment. Kaine voted against the original version of the bill, as did all but four Senate Democrats, and voted for the compromise.

Current proposals in Congress

Although abortion has long been a polarized issue, with almost all Republicans pro-life and almost all Democrats pro-choice, enough pro-choice Democrats have been ambivalent about taxpayer financing to prevent the Hyde Amendment from being repealed, despite repeated attempts to do so. The closest it came was in 1993, after newly elected President Bill Clinton had campaigned for repeal, but the amendment was maintained by a vote of 255–178.

Last Congress, the Republican-led House passed a measure that would have made the Hyde Amendment permanent. The No Taxpayer Funding for Abortion and Abortion Insurance Full Disclosure Act, H.R. 7 (113th Congress), passed the House 227–188 in January 2014, with one Republican voting against and six Democrats voting in favor. However, the bill never received a vote in the Senate, controlled by Democrats at the time. Democrats wryly noted that of the House Judiciary Committee Republicans who voted to advance the bill out of committee, all 22 were men.

In this Congress, the H.R. 7 legislation with the same title passed the House in January 2015 by 242–179, with one Republican against and only three Democrats for. The Senate equivalent bill S. 852 has still not received a vote, despite 43 Senate Republicans co-sponsoring.

The bill in this Congress to expand access to abortion services is H.R. 2972, the Equal Access to Abortion Coverage in Health Insurance (EACH Woman) Act. It would allow federal taxpayer dollars to be used for most abortions, beyond the existing limited exceptions for rape, incest, and life of the mother. The bill has not received a vote and is unlikely to under a Republican-controlled Congress, but has received 119 Democratic cosponsors. This indicates that the legislation likely has enough votes to pass under a potentially Democratic-controlled House next year.

Is the Hyde Amendment constitutional?

Although the amendment was originally passed in 1976, it didn’t go into effect until 1980 after the Supreme Court upheld it as constitutional in the 5–4 decision Harris v. McRae. The court’s majority wrote, “Regardless of whether the freedom of a woman to choose to terminate her pregnancy for health reasons lies at the core or the periphery of the due process liberty recognized in Wade, it does not follow that a woman’s freedom of choice carries with it a constitutional entitlement to the financial resources to avail herself of the full range of protected choices.”

It’s not clear whether the Court would still uphold that same reasoning today. Not only was the original margin razor-thin, but last month the Court struck down abortion restrictions in Texas in what was hailed as their most pro-choice decision in at least a decade. And the Court may swing further to the left still if Hillary Clinton wins the presidency and the Democrats take back the Senate.

This article was written by GovTrack Insider staff writer Jesse Rifkin.