Four former Blackwater security guards face decades in prison when they are sentenced Monday for their roles in a 2007 shooting of Iraqi civilians.

Three of the guards -- Dustin Heard, Evan Liberty and Paul Slough -- face mandatory, decades-long sentences because of firearm convictions. A fourth, Nicholas Slatten, faces a life sentence after being found guilty of first-degree murder.

The men were charged in the deaths of 14 Iraqis at Nisoor Square, a crowded traffic circle in downtown Baghdad. The killings caused an international uproar, and the men were convicted in October after a legal fight that spanned years.

Prosecutors have described the shooting as an unprovoked ambush of civilians, though defense lawyers countered that the men were targeted with gunfire from insurgents and Iraqi police, and shot back in self-defense.

The lawyers are expected to argue for mercy Monday by saying that decades-long sentences would be unconstitutionally harsh punishments for men who operated in a stressful, war-torn environment, and who have proud military careers and close family ties.

The sentencing hearing arrives with much at stake for the men, given the heavy punishments the government is seeking. The firearms convictions alone carry mandatory minimum sentences of 30 years in prison. But the government is seeking sentences far beyond that, partly because they say the men have never shown remorse or accepted responsibility. The murder conviction against Slatten carries a life sentence.

Regardless of the sentences, the hearing certainly won't bring an end to the legal wrangling, which began even before the guards were first charged in 2008. A judge later dismissed the case before trial, but a federal appeals court revived it and the guards were indicted again in October 2013.

Even before the trial began, defense lawyers had identified multiple issues as likely forming the basis of an appeal, including whether there was proper legal jurisdiction to charge them in the first place.

The statute under which they were charged, the Military Extraterritorial Jurisdiction Act, covers the overseas crimes of Defense Department civilian employees, military contractors and others who are supporting the American war mission. But defense lawyers note that the Blackwater defendants worked as State Department contractors and were in Iraq to provide diplomatic, not military, services.

The legal fighting continued in the days leading up to sentencing, too, with defense lawyers seeking Friday to postpone the hearing after receiving new information -- a victim impact statement from a trial witness -- that they said was favorable to the defense.  But a judge denied the request, saying there was no need to delay the sentencing.