A pack of civil rights and criminal justice reform groups are teaming up to target St. Louis in a class action lawsuit challenging a pretrial system that leaves people trapped behind bars with no recourse if they don't have the money to pay for bail.

It's the latest salvo in the legal push to try to force court systems across the country to reform the way they handle people who have been charged with crimes, but not yet been convicted. Several court systems and judges have turned to a dependency on bail schedules that require defendants to pay sometimes excessive amounts of money (either directly to the courts or a smaller amount to a bail bondsman) in order to be freed from jail before their trials.

The system has come under attack because in many communities, judges or magistrates rarely give any consideration to a defendant's ability to pay bail. So across the country there are thousands of people stuck in jail cells not because they're deemed flight risks or dangers to society—the ostensible reason why courts are asking bail in the first place—but because they simply don't have the money to pay bail.

On Monday, St. Louis-based ArchCity Defenders, teaming up with the Advancement Project, the Institute for Constitutional Advocacy and Protection at Georgetown Law, and the Civil Rights Corps, filed a class action federal lawsuit arguing that the city's bail system leaves people trapped in jail and punishes them because they're poor, violating their constitutional rights.

The lawsuit has been filed on behalf of four men who are detained at the City Workhouse, St. Louis' medium security detention center. According to the lawsuit, these men were arrested and told they would remain in custody unless they coughed up thousands of dollars for a bond. At no point were they asked about their ability to pay, nor were they able to plead their case. One plaintiff said a judge would cut off anybody who attempted to speak or explain that they couldn't afford the bond.

According to the lawsuit, defendants who cannot pay the bond demanded of them can be left in detention for weeks because they won't get a release hearing until they have counsel. For those who need a public defender, it can take four to five weeks for get one appointed. As a result of these practices, about 85 percent of the more than 1,000 defendants locked up in St. Louis jails are there because they cannot afford the bail that has been demanded of them, according to the suit.

The lawsuit is asking that the court declare that this pretrial detention system violates defendants' equal protection and due process rights, and they're seeking an injunction to stop St. Louis from jailing people just because they cannot afford to pay their bond.

In a press conference announcing the lawsuit Monday, ArchCity Defenders Executive Director Blake Strode noted, "Simply put, these men have been condemned to be locked in cages for weeks, solely because they are poor…The de facto detention orders issued by this circuit have cost thousands of people their homes, jobs, custody of their children, and much more."

Read the lawsuit for yourself here. And read more about the alternatives to cash bail systems and the challenges implementing them here.