Washington (CNN) The Department of Justice has announced it will evaluate immigration judges on how many cases they close and how fast they hear cases, a move that judges and advocates criticize as potentially jeopardizing the courts' fairness and perhaps leading to far more deportations.

The policy has been in the works for months, as Attorney General Jeff Sessions and the Trump administration have been working to assert more influence over the immigration courts, or the separate court system built just for hearing cases about whether noncitizens have a claim to stay in the US.

US law gives the attorney general broad and substantial power to oversee and overrule these courts, as opposed to the civil and criminal US justice system, which is an independent branch of government. In the immigration courts, judges are employees of the Department of Justice.

Sessions has been testing the limits of that authority in multiple ways, and in a memo Friday, the director of the immigration courts informed judges they would now be evaluated on a set of metrics including the speed and volume of cases heard.

The Justice Department says the move is designed to make the system more efficient. The immigration courts have a backlog of hundreds of thousands of cases, and it can take years for an immigrant's case to work its way to completion. In that time, the individuals build lives in the US, and critics point to the immigration courts' backlog as a major factor in the number of undocumented immigrants living in the US.

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