Jefferson City. Mo. ? Opponents of a new state law requiring voters to show government-issued photo identification filed a second lawsuit Thursday, claiming it could discourage or prevent people from voting in November.

The challenge filed in Cole County Circuit Court seeks a preliminary injunction to block the law from taking effect Aug. 28 and wants the law declared unconstitutional.

“This requirement imposes an unnecessary, unauthorized and undue burden on the fundamental right to vote of at least 170,000 registered Missouri voters who do not currently possess a photo ID,” the lawsuit said.

Plaintiffs include several voters who say they lack an acceptable ID under the new law and therefore could not cast a regular ballot in the Nov. 7 general election.

Republican Gov. Matt Blunt has praised the new law as a way to build public trust in elections.

Last month, Democrats in St. Louis and Kansas City filed a lawsuit claiming the law unconstitutionally imposes costs on local governments without providing state funding. No hearing has been set.

The challenge filed Thursday said the photo ID requirement infringes on the fundamental right to vote under the Missouri Constitution, and claims it disproportionately harms black and female voters, along with the poor, elderly or disabled who may not drive and have no license.

The requirement also imposes illegal costs on those trying to obtain a photo ID, the suit said. The ID is free, but applicants must show paperwork such as a birth certificate to prove they are in the country lawfully, which costs $15 to obtain for people born in Missouri.

Married women could be particularly affected, the suit said, because they need extra documents for an ID card if their birth certificate is not in their current name.

The suit alleges that supporters of the ID requirement want to prevent minorities and others who tend to support Democrats from voting. The state Democratic Party is backing the suit financially.

“It is no surprise that Democrats are again rushing off to the courthouse to oppose a law that ensures honest elections under sensible, evenhanded rules,” Republican Party spokesman Paul Sloca said in a statement.

A federal judge last month blocked the state of Georgia from enforcing its new voter ID law this year. The judge said Georgia’s photo ID requirement discriminated against people who don’t have driver’s licenses, passports or other government identification.

In April, though, another federal judge ruled that Indiana’s photo ID law could stand because Democrats failed to show it was too burdensome. Voters in a May primary election were required to show a state or federally issued photo ID card before casting ballots.