JEFFERSON CITY, MISSOURI - A Missouri judge on Tuesday blocked key portions of the state's voter photo identification law, meaning some voters could find it easier to cast ballots in a November election headlined by a hotly contested U.S. Senate race.

The ruling bars election officials from enforcing a requirement that a voter lacking a valid photo ID sign a sworn statement while presenting some other form of identification in order to cast a regular ballot. It also prevents the state from advertising that a photo ID is required to vote.

The permanent injunction by Senior Cole County Circuit Judge Richard Callahan takes effect immediately. But Republican Secretary of State Jay Ashcroft said he plans to ask that the ruling be put on hold while he appeals to a higher court.

The case will affect voting procedures in the general election that is headlined by a race between Democratic U.S. Sen. Claire McCaskill and her Republican challenger, Attorney General Josh Hawley, whose office defended the state law on behalf of Ashcroft.

Voter photo ID requirements have been pushed by Republicans in numerous states as a means of preventing fraud. They have been opposed by Democrats who contend such laws can disenfranchise poor, elderly, disabled and minority voters who are less likely to have photo IDs.

Attorneys for Priorities USA, a Washington-based liberal advocacy group that sued on behalf of some Missouri voters, argued that more than 300,000 voters may lack valid photo identifications. As of last week, the state had issued free photo identification cards to 1,456 voters who requested them.

Priorities USA Chairman Guy Cecil praised the ruling as 'an important victory for voting rights that will ensure that future elections in the state are open and accessible to every eligible voter.''

Missouri's 2016 law was enacted when the Republican-led Legislature overrode the veto of then-Gov. Jay Nixon, a Democrat. Voters in 2016 also approved a constitutional amendment intended to permit photo identification laws. The Missouri law was not yet in effect for the 2016 elections.

Callahan's ruling doesn't invalidate Missouri's entire law, which states that voters shall establish their identity with a valid government-issued photo identification. But the ruling could knock out some of the law's teeth.

The law had allowed people lacking a photo ID to cast regular ballots if they show one of several non-photo forms of identification and sign sworn statements saying they don't possess personal identification, understand they can get an ID for free from the state and acknowledge that personal identification is required to vote.

Callahan said the sworn statement is 'contradictory and misleading'' and 'impermissibly infringes on a citizen's right to vote as guaranteed under the Missouri Constitution.'' During arguments last week , Callahan said that such a written statement would be confusing for his elderly mother, who no longer has a valid driver's license and lives in a facility in a different county from where she owns a home.

It's not clear from Callahan's ruling whether the secretary of state's office could come up with a new version of the affidavit that could be required in elections. Otherwise, the ruling appears to allow people lacking photo IDs to nonetheless cast regular ballots if they show some other form of identification, such as a student ID card, utility bill, bank statement or paycheck that contains a home address.

The ruling leaves in place another option for people lacking identification to cast provisional ballots, which are counted if their signatures match those on file or they return later to show a photo ID.

Hawley spokeswoman Mary Compton said the attorney general's office is 'reviewing the ruling and will continue to vigorously defend Missouri's commonsense voter ID law.''