In 2008 the UK government passed a law making it compulsory for all companies to automatically enrol some of their employees into a workplace pension scheme.
Once enrolled, a small % of the employee’s salary would go into their pension, and the employer would add some more on top.
Companies were given some time to get started depending on how big they were, but by 2018 the new law applied to every employer in the UK.
To qualify for auto-enrolment you must be between 22 - state pension age and earn more than £10,000 a year.
Your employer can't encourage/force you to opt out or unfairly dismiss or discriminate against you for being in the workplace pension.
There are some instances where an employer doesn't have to automatically enrol you and these rules are subject to the UK Government. For more information, please visit their website: https://www.gov.uk/workplace-pensions/joining-a-workplace-pension