WASHINGTON — A U.S. senator wants to know how well the country’s top six voting machine manufacturers protect themselves against cyberattacks, a move that comes just weeks after federal authorities notified 21 states that they had been targeted by Russian government hackers during the 2016 presidential election

In a letter Tuesday to the CEOs of top election technology firms, Sen. Ron Wyden writes that public faith in American election infrastructure is “more important than ever before.”

An assessment by the Department of Homeland Security found that Russian hackers targeted state election systems. Some states have since disputed that claim.

A representative for Election System & Software said the company had not yet received Wyden’s letter.