This is just asking to join a workplace pension scheme under the auto-enrolment rules.
Depending on your age and earnings, you might not be put into your employer’s workplace pension scheme automatically, but you can still ask to join if you’d like to.
And if you’ve previously asked to leave (opted out or ceased active membership), you can ask to join again. (Though if it’s within the same year you asked to leave, you’ll have to get your employer to agree first.)