Just hours after news of Justice Anthony Kennedy’s retirement broke, advocacy groups called on Senators to block any replacement opposed to LGBTQ equality.

As was long anticipated, the 81-year-old justice announced he will be retiring at the end of the 2018 term. A moderate conservative appointed by Reagan, Kennedy served as a liberal swing vote on many of the Supreme Court’s most progressive rulings on LGBTQ rights, authoring the majority opinions in the Lawrence v. Texas decision striking down state sodomy bans and the Obergefell v. Hodges verdict legalizing marriage equality.

During the 2016 election, President Donald Trump vowed to appoint judges to the Supreme Court who would overturn its 2015 ruling on same-sex marriage. After tapping Justice Neil Gorsuch last year, the POTUS will now have a chance to fill another seat.

LGBTQ advocates and their allies urged lawmakers to oppose any Supreme Court nominee who would help Trump follow through on that promise.

“Whoever is confirmed to the seat will serve for life, and the values they bring to the job will shape our country for a generation,” said People For the American Way President Michael Keegan in a statement. “The stakes for this nomination couldn’t be higher, and Senators should make clear that they’ll oppose any nomination that isn’t the result of meaningful bipartisan consultation.”

Others argued the Senate should block any Trump appointee until after the 2018 midterms.

“The stakes for the next nomination are too high for our community to sit back and let the White House ram through another anti-LGBTQ extremist,” said Rick Zbur, executive director of Equality California, in a statement. “It is incumbent upon all of us to ensure Justice Kennedy’s replacement is willing to stand up to the Trump-Pence Administration and protect our civil rights.”

“We urge every member of the U.S. Senate who supports equality and social justice for the LGBTQ community, for women, for immigrants and for communities of color to refuse to confirm any nominee until after the November midterm elections,” he added.

Other LGBTQ groups agreed with that assessment.

“We cannot allow 40 more years of Trump’s values on the Supreme Court,” said Lambda Legal CEO Rachel Tiven said in a statement. “Attempts by President Trump and Vice President Pence to use a new court vacancy as a way to deprive us of our dignity, to demean our community, or to diminish our status as equal citizens will be met with a chorus of opposition from civil rights leaders across the country.”

“Now more than ever, we need all Senators, including principled moderate Senators, to hold the line to prevent any nominee who would fail to ensure our country’s most basic principles of justice and equality for all,” added National Center for Lesbian Rights (NCLR) Legal Director Shannon Minter.

There is relatively recent precedent for members of the Senate intentionally delaying the vote on a president’s Supreme Court pick.

When President Obama tapped Merrick Garland to replace the late Antonin Scalia in March 2016, conservatives in the Senate Judiciary Committee stated in a letter to Majority Leader Mitch McConnell that they would “exercise [their] constitutional authority to withhold consent on any nominee to the Supreme Court submitted by this president.” The 11 signatories included Sens. Ted Cruz, Lindsey Graham, and Jeff Sessions.

Blocking a replacement for Scalia for more than a year paved the way for Gorsuch, an arch-conservative jurist who opposed same-sex marriage in his 2004 dissertation at Oxford University.

Since joining the Supreme Court last year, Gorsuch has sided against LGBTQ equality in every case that has come before the nation’s highest bench. When SCOTUS issued a “narrow” 7-2 ruling in the case of an anti-gay baker who denied a wedding cake to a same-sex couple, he was part of a conservative contingent that wanted the ruling to go further—and issue a license to discriminate against LGBTQ people.

Gorsuch was joined in that opinion by Justice Samuel Alito.

As the court weighs in on issues of “religious liberty” and other key battles down the line, advocates claimed it was critical to ensure the White House doesn’t have the power to continue to rollback LGBTQ rights through the courts—as Trump has consistently done since taking office.

“The next justice could cast pivotal votes on whether it is legal to fire a transgender employee, target transgender students at school, or refuse health care to transgender patients,” said National Center for Trans Equality Executive Director Mara Keisling in a statement. “Unfortunately, every member of President Trump’s ‘shortlist’ has been vetted to ensure they will not uphold these basic rights.”

Previous Supreme Court candidates put forward by the Trump administration include Diane Sykes, who argued that university groups which discriminate against LGBTQ students should still have the right to funding from their college, and William Pryor, who supports laws criminalizing homosexuality.

Nearly one-third of all judicial nominees appointed by Trump have a noted record of opposing LGBTQ rights, according to Lambda Legal.

The difference between Garland and any nominees tapped by Trump, however, is that Republicans held a majority in the Senate in 2016. Democrats—who occupy 49 seats in the upper house of the legislature—do not hold that bargaining power alone and will need conservatives to join them in preventing a SCOTUS appointment. In addition, Senate Republicans altered procedural rules following the standoff over Garland making it more difficult for Democrats to filibuster in the future.

McConnell has pledged a vote on Kennedy’s replacement by the fall.