Sen. Kirsten Gillibrand, D-N.Y., has vowed to no longer accept campaign contributions from corporate PACs, she announced Tuesday.

With the new pledge, taken in conjunction with the group End Citizens United, Gillibrand became the fourth sitting U.S. senator to reject corporate PAC money, joining Sens. Bernie Sanders, I-Vt., Elizabeth Warren, D-Mass., and Maria Cantwell, D-Wash.

“Because of the corrosive effect of corporate money in politics, I’ve decided from this point on I am no longer accepting corporate PAC checks into my campaign,” Gillibrand said in a video announcing her decision. “We have a system where corporations can spend unlimited money that isn’t even disclosed, so there’s no transparency.”

According to Open Secrets, which tracks campaign contributions, the Democratic senator accepted $4.9 million from business PACs from 2005-2018. Gillibrand said her worry about corporate money in politics stems from the 2010 U.S. Supreme Court ruling in Citizens United v. Federal Election Commission, which found the government cannot restrict political contributions from corporations.

The New York senator, who is up for re-election this year, received an endorsement from End Citizens United after announcing her promise to no longer accept money from corporate PACs.

Gillibrand touted her record of transparency since she was first elected to the U.S. House in 2006, which includes publishing her schedule, requests for earmarks, financial disclosures, and tax returns. She was appointed to fill the Senate seat held by Hillary Clinton in 2009. Rejecting donations from corporate PACs, she said, is the latest step to ensure transparency and accountability.

“We really need to make every effort we can to get rid of the corporate money and dark money that is flowing into politics, and my effort to ban corporate PAC checks is just the first step in that direction,” Gillibrand said.

End Citizens United has endorsed 18 other Senate candidates, including 14 incumbents.