Sen. Susan Collins (R-Maine) is coming under fire for her 2018 vote to confirm Supreme Court Justice Brett M. Kavanaugh, after Kavanaugh dissented in Monday’s landmark ruling affirming that federal anti-discrimination laws protect gay and transgender employees.

Collins, who faces a tough 2020 reelection bid, is among the most vocal Senate Republican supporters of LGBTQ rights. She is one of the lead sponsors of the Equality Act, which would add sexual orientation and gender identity to other protected classes in federal law. After news of Monday’s 6-to-3 Supreme Court decision was reported, she praised the ruling as “a major advancement for LGBTQ rights” and called for Congress to pass the Equality Act and amend the Civil Rights Act to “expressly prohibit” such discrimination.

But Democrats — including Maine House Speaker Sara Gideon, Collins’s likely general election opponent — skewered Collins on Monday for her vote to confirm Kavanaugh in light of his position on Monday’s ruling.

“Judge Kavanaugh voted against banning companies from firing employees for being gay or transgender,” Gideon said in a tweet. “It’s clear that Senator Collins will continue to be a reliable vote for Trump’s anti-LGBTQ+ nominees. Help us replace her in November.”

Collins also faced criticism last year after the Supreme Court voted 5 to 4 to block a restrictive Louisiana abortion law. While Democrats hailed the decision, they pointed to Kavanaugh’s dissent as a sign that he might be poised to side with conservatives in future rulings on abortion rights.

In October 2018, Collins delivered a 44-minute floor speech declaring her support for Kavanaugh. At the time, Collins, who supports abortion rights, said she did not think Kavanaugh would vote to overturn the landmark 1973 Roe v. Wade ruling that legalized abortion nationwide. She also noted in her speech that Kavanaugh “described the Obergefell decision, which legalized same-gender marriages, as an important landmark precedent.”

Quoting a previous decision, Kavanaugh wrote in his Monday dissent that the Supreme Court “has previously stated, and I fully agree, that gay and lesbian Americans ‘cannot be treated as social outcasts or as inferior in dignity and worth.’ ”

But he argued that under the Constitution’s separation of powers, it is “Congress’s role, not this Court’s,” to amend Title VII of the Civil Rights Act of 1964, which prohibits discrimination “because of sex.”

“Our role is not to make or amend the law,” he wrote. “As written, Title VII does not prohibit employment discrimination because of sexual orientation.”

Collins’s office pointed to the senator’s record of voting to confirm not just Kavanaugh but all six Supreme Court nominees who have been considered during her time in the Senate.

Two of those justices — Chief Justice John G. Roberts Jr. and Justice Samuel A. Alito Jr. — were nominated by President George W. Bush. Two others — Sonia Sotomayor and Elena Kagan — were nominated by President Barack Obama. Kavanaugh and Neil M. Gorsuch were nominated by President Trump.

Robert Barnes contributed to this report.