The lawsuit from state Attorney General Josh Shapiro seeks to block the subpoena on the grounds that it serves no legitimate legislative purpose and stems from Trump's efforts to undermine trust in the results of the 2020 presidential election.
Democrats had said they would sue within days after the Republicans voted last week to seek detailed state election records for an audit they claim has nothing to do with Donald Trump.
Republicans in Pennsylvania's state Senate insist the undertaking has nothing to do with Donald Trump or trying to overturn last year's presidential election.
The legal challenge is the latest attempt by Republicans to invalidate the 2019 law that Republican lawmakers almost unanimously supported.
Rick Saccone drew attention Jan. 6 when he posted videos from outside the US Capitol that appeared to support the violent insurrection by supporters of then-President Donald Trump.
Will there be an election audit in Pennsylvania? Could the results be overturned? Why is this even happening? Answers to these questions and more.
The county said it had complied with the guidance in force at the time for the inspection of voting machines by third-party vendors.