Only staff that who meet the following criteria are to be enrolled:
1. Earn over £192 per week (or £833 per month)
2. Aged 22 or over and
3. Under state pension age.
They can opt out but do not try persuading staff as it is against the law.
Go for Government schemes like Nest Pensions or others, you do not pay any fees on top of your contributions. Some Pension Companies have built in costs for administering the scheme with average cost of £8,000.
And ensure you keep upto date records.