A group of former prisoners in Florida are suing over what they call an attempt by Republicans to restrict democracy and undo a historic initiative restoring the right to vote to 1.4m previously incarcerated felons.

Last year, Floridians gave their approval to the initiative, known as amendment 4, one of the most influential voting rights amendments in state, if not national, history. Allowing ex-felons to cast a ballot has the potential to shift the balance of power in Florida, which has plumped narrowly for Republican candidates in recent major elections, by adding a significant population of voters back into the mix.

But voting rights advocates were not able to celebrate for long. Months after Governor Ron DeSantis gave his tepid approval to amendment 4, the state’s Republican legislature introduced a bill that would require the newly eligible population to pay every court fee, fine and lien they might have faced during and after their conviction in order to vote. Amendment 4 supporters called the new law a dangerous “poll tax” designed to disenfranchise voters of color. DeSantis signed the bill into law in the summer.

On Monday, the former felons, along with the ACLU and others, filed an injunction calling the new law unconstitutional. “The ability to vote [under this law] becomes based on your pocketbook, how much money you have,” said Melba Pearson, the legal director of the ACLU Florida chapter. “If you’re not able to pay fines or fees you would be prohibited from voting. That’s, quite frankly, wrong.”

While US states have historically curbed the right to vote among incarcerated populations, Florida’s terms have been especially restrictive. States such as Maine and Vermont allow incarcerated people to vote while in custody, and 14 other states restore voting rights upon release.

The trial comes at a crucial time, with municipal and primary elections due across Florida in the coming weeks and the presidential election a year from now. The state went for Donald Trump in 2016 by a narrow margin. As with the rest of the state, ex-felons do not tend to vote for any particular party over another, and Pearson emphasized that this was a nonpartisan issue.

Mark Mauer, the executive director of The Sentencing Project, a research and advocacy organization focused on the rights of incarcerated populations, cited estimates that upwards of 80% of the people who completed their sentences would be blocked from voting if the law is implemented. “Most are indigent and low income,” he said. “This level of fines and fees imposed completely beyond their ability to pay.”

The trial is expected to last through the week, but Pearson of the ACLU said blocking the law is only part of the process. “The battle in court will continue with regards to the constitutionality of 7066,” she said, referring to the law’s designation. “We have to ensure this will not prohibit voting in the primaries.”