After President Donald Trump called for a $1.5 trillion infrastructure plan in his State of the Union address, senators from states surrounding Washington, D.C., said it should include money for the city’s public transportation system.

Four Democratic senators — Mark Warner and Tim Kaine of Virginia, and Benjamin L. Cardin and Chris Van Hollen of Maryland — wrote a letter to the administration on Friday asking it not only to maintain the funding already in place for the Washington Metropolitan Area Transit Authority, known locally as Metro, but to add more for improvements.

The letter, addressed to Office of Management and Budget Director Mick Mulvaney and Transportation Secretary Elaine Chao, warned that the Metro will have to forgo critical safety improvements if it loses federal funding.

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Funding is up in 2019 after the Passenger Rail Investment and Improvement Act of 2008 gave the transit authority $150 million in yearly federal funds, totaling $1.5 billion for a 10-year period.

In 2016, senators made a similar plea to the Obama administration, asking for continued funding of $150 million a year.