The New Orleans Civil Service Commission has approved changes proposed by Mayor Mitch Landrieu.
The Fraternal Order of Police immediately sued.
Nola.com/The Times Picayune reports the group is asking a Civil District Court judge to block the overhaul. The group says the move will bring political favoritism into the process.
The administration says employees will be protected while managers will be able to hire the best employees.
Managers have been bound by a rule requiring a selection be made from three top candidates scored by the Civil Service Commission staff.
Landrieu wants department heads to be able to hire anyone meeting minimum qualifications, as long as they can justify their choice.