Pre-employment or random screening is illegal in several European nations. While most allow use in safety-critical locations, some have put precautions in place. In the aviation, rail, and shipping sectors, drug testing is required by law.
When a business does background checks on all prospective workers or candidates before hiring them, this is referred to as pre-employment screening. People are more vulnerable during this period because they are unemployed and have fewer employment rights, are not protected by grievance or appeals processes, and lack the backing of a union. Many companies choose this kind of testing since it is less expensive and only has to be done once. However, since it is usually dependent on a urine sample, diluting or replacing the sample is frequently easier because it must be given in secret.
When an employer does post-event testing, it is done after an incident that results in an injury, property damage, or a near miss. This is sometimes done automatically after an event, but only if the supervisor believes drugs had a role. This is often used to release an employer from responsibility if an employee gets injured on the job. They will argue that the employee was under the influence of drugs at the time of the injury.
Choosing and testing a random sample of workers at regular intervals is known as random testing. Drug testing companies claim it is a significant deterrent, but it has been argued that in the United States, where it is far more widespread, users are more likely to switch from cannabis (which remains in the urine for considerably longer) to harsher drugs, which disappear from the system much quicker.