The Federation Police Force (also called Galactic Federation Police, Galaxy Federal Police, Federation Police or Federal Police) is a military organization founded by the Federation Bureau created specifically as a response to the Space Pirates' attacks on vessels. Despite being powerful a force, the vastness of space has made locating the Pirates extremely difficult, as such they and the Federation Bureau pay high prices to powerful bounty hunters to assist them.
Samus, along with Mauk and Kreatz, was once a member of the Federation Police and had Adam Malkovich as her CO. Eventually Samus left the police force to become a bounty hunter. Chief Hardy is the chief of the Federation Police.
The Federation Police decide to send Samus when they fail to take Zebes, and she succeeds on her own during her Zero Mission. At some point after these events, it was determined that the Metroids needed to be destroyed once and for all. According to the manual to Metroid II, a research team was sent to check on SR388. When contact with this team was lost, the Federation Police then proceeded to send a rescue party and then a platoon of heavily armed soldiers to the planet, both of which were lost. However, the manual for Super Metroid and the introductory cutscene to Samus Returns states that, following Samus' attack on Zebes, there was only a single expedition to SR388 with the goal of wiping out the Metroids. In both cases, the Galactic Federation Council then gave Samus Aran the order to go to SR388 and exterminate the Metroid population.
The Federation Marines and the Galactic Federation Army mentioned in Metroid: Zero Mission and seen in the Prime series and Metroid: Other M effectively replaced the police for a time. However, in Metroid: Samus Returns, the Galactic Federation Special Squadron sent to SR388 is said to be a part of the police force.