NASHVILLE (AP) — Advocates for expanding school choices in Tennessee faced their first major road block Thursday after the state's largest communities filed a lawsuit seeking to block a new voucher program from going into effect later this year.

Nashville Mayor John Cooper announced his office filed the complaint with the support of Nashville's Board of Public Education.

"You and I both have the concern of having a stable financial platform for the funding of our schools and this case will go to the heart of that," Cooper told school board members during a hastily assembled meeting scheduled to unveil the lawsuit.

"Laws should be good enough to apply equally to everybody and we do have the right to ask a court about this being unfair to us," Cooper added, as a handful of Republican state lawmakers and voucher proponents sat behind him.

Shelby County, which encompasses Memphis, is also a plaintiff. Republican Gov. Bill Lee and his handpicked education commissioner, Penny Schwinn, are named as defendants.

The lawsuit comes less than a year after Lee signed the school voucher bill into law with narrow support from the GOP-controlled Statehouse and strong opposition from Democratic members and public education advocates.

The law would begin diverting tax dollars to private education, starting in the 2020-21 school year, by allowing participating families to receive up to $7,300 in state education money each year.

The program, which establishes education savings accounts, would apply only to the state's largest school districts — Nashville metro and Shelby County, the areas with the lowest performing schools and regions with Democratic political strongholds.

The original version of the measure included several other counties, but it was eventually whittled down after Republican lawmakers objected due to uneasiness about launching a voucher program in their own legislative districts.

The governor's office did not immediately responded to a request for comment. The education commissioner and Tennessee's attorney general office declined to comment on the pending litigation.

The 44-page suit alleges the voucher law is illegal under the Tennessee Constitution's "home rule." It claims that Republican lawmakers did not receive local consent when drawing legislation affecting local communities.

"If this is good policy, then vouchers should be available to students in struggling schools across the state," said former Tennessee Attorney General Bob Cooper, who is now Nashville's law director. "But the legislative record makes clear that the general assembly's decision to impose vouchers only on Davidson and Shelby counties was based on politics, not policy."

Opponents go on to argue it violates another provision in the state constitution by "diluting public school funding" for just Davidson and Shelby counties and not all of the state's 95 counties.

Also tucked inside the complaint is a meticulous retelling of how the voucher proposal was passed by lawmakers last year, pointing to one Republican who said she would only vote in favor because it didn't affect her legislative district.

Another Republican boasted at the time that the voucher law would ensure "that our poorest children in those deep blue metropolitan areas have a fighting chance at a quality education."

Republican legislative leaders on Thursday described the lawsuit as puzzling.

"I will remind for those interested that this a very limited pilot program ... in those two districts for students trapped in failing schools where they are not receiving an adequate education and this will give them an opportunity to go to be a better school," said Senate Majority Leader Jack Johnson.

While some call the voucher measure a "pilot program," the law does not include a sunset clause detailing when — or if — it would ever shutter.

The lawsuit does not, however, address the legality of the voucher program's income verification — which requires participating families to provide federal income tax returns showing they do not exceed twice the federal income eligibility for free school lunch, or provide proof they can qualify for federal assistance.

Separately, the American Civil Liberties Union of Tennessee and the Tennessee Immigrant and Refugee Rights Coalition have said the law would exclude families who are in the U.S. illegally from getting their children vouchers. No lawsuit targeting that angle has yet been filed.