Final answer:
Travel may be denied for PRM due to international travel restrictions, criminal investigations, and government disapproval, or because of internal movement controls like China's hukou system and social credit system.
Step-by-step explanation:
Travel may be refused for persons with reduced mobility (PRMs) for a variety of reasons related to both international travel restrictions and internal movement controls within a country. In general, countries use passports as a control mechanism to regulate the exit and re-entry of citizens. Conditions for obtaining a passport can vary, and even those with a passport may face travel restrictions. For instance, individuals under criminal investigation or those on a terrorist watch list may be barred from international travel. Specified groups that a country's government disapproves of, such as the Uyghurs in China, may also need official permission to travel, which is rarely granted. Furthermore, China's hukou system limits the internal movement of many internal migrants, and police checkpoints restrict certain ethnic groups. The social credit system may also regulate an individual's right to travel both domestically and internationally by requiring points to be earned for travel privileges.