A state court in Pennsylvania on Friday struck down the state’s landmark election law as unconstitutional, dealing a temporary blow to voting access in one of the nation’s most critical battleground states.

The law, known as Act 77, was passed by the Republican-controlled legislature and signed by Gov. Tom Wolf, a Democrat, in 2019. It permitted no-excuse absentee voting, created a permanent mail-in voter list, reduced the voter registration deadline from 30 days to 15 and provided for $90 million in election infrastructure upgrades. It also eliminated straight ticket voting.

The opinion from Judge Mary Hannah Leavitt, a Republican, sided with 14 Republican lawmakers who sued last year, arguing that the law was unconstitutional and that the legislature could not make alterations to voting laws without amending the constitution.

The bipartisan law was praised by both sides when it was passed, but it became a target of conservatives during the 2020 election, as former President Donald J. Trump unspooled falsehoods and lies about mail-in voting. Eleven of the 14 lawmakers who sued to kill the law had voted for it in 2019.

Democrats said they were not surprised that the Commonwealth Court, which they said leans Republican, ruled against the law, and they pledged an appeal to the state Supreme Court, which has sided with the state on voting issues both during and following the 2020 election.

“This is just a continuation of attacking and undermining our electoral process,” said State Senator Jay Costa, the Democratic minority leader. He added that an appeal would be filed by the end of the day. “Act 77 will ultimately be deemed to be constitutional.”