CLAYTON, Mo. -- Two protesters arrested in Ferguson during protests last year are challenging the St. Louis County ordinance cited in their arrest, calling it too vague.

The Rev. Melissa Bennett and KB Frazier filed suit against the county, county counselor Peter Krane and Missouri Attorney General Chris Koster, claiming the ordinance violates their 14th Amendment rights and should be tossed out.

Both were among many protesters cited for interfering with police, but the lawsuit states the ordinance does not define adequately what constitutes interference.

County officials said the ordinance does not violate free speech, but simply requires some order be maintained.

Ferguson was the site of protests after 18-year-old Michael Brown, who was black and unarmed, was shot to death by officer Darren Wilson.

The shooting fueled the national Black Lives Matter movement.

Maggie Ellinger-Locke, the lawyer for Bennett and Frazier, said the ordinance never defines interfering or obstructing, the St. Louis Post-Dispatch reported.

"The arbitrary application of this ordinance cannot be left entirely to an officer's discretion, and protesters need to know if or when they're in violation of the law," she said.

Frazier and Bennett were protesting against police brutality when they were arrested Oct. 22, 2014.

Charges were filed in July but were dropped before the case went to trial.

The charges allege they "unlawfully interfered in any manner with a police officer or other employee of the County in the performance of his official duties or obstructed him in any manner whatsoever while performing any duty to wit, by walking and standing in the roadway after being warned not to do so by the police officer."

Ellinger-Locke asked St. Louis County Circuit Judge Gloria Clark Reno to issue a preliminary and permanent injunction to prevent enforcement of the ordinance, which she said had a "chilling effect" on protesters.

Assistant county counselor Carl W. Becker said the suit doesn't belong in St. Louis County, but in federal or municipal court.

He noted Frazer protested again, including taking part in an interstate highway shutdown.

"It clearly didn't have a chilling effect," Becker said.

Reno gave both sides a month to submit more information.

It isn't clear when she will rule.