The ability of workers to change jobs. This may be between different firms, different occupations, different locations, or different countries. There can be a range of obstacles to mobility. Workers changing employers lose seniority, which may affect their pay, vacations, and redundancy rights, and may lose in terms of their pension rights. Workers changing occupations lose in terms of the weight given to their experience and possibly to their formal qualifications. Workers changing location face problems over housing. International mobility of labour is hindered by immigration controls, problems over recognition of the immigrants’ qualifications, and language barriers. Governments and supra-national organizations such as the European Union attempt to improve labour mobility in the interests of economic efficiency, but perfect mobility of labour seems extremely unlikely. See also factor mobility.