Yes. If you are auto-enrolled into your umbrella employer’s workplace pension scheme, you can opt out at any time.
If you choose to opt out of the scheme within one month of being automatically enrolled, you will be treated as if you had never joined the scheme. Any money that you have paid into the scheme will be refunded in full. You’ll only receive back the payments that you are deemed to have made, so you’re not entitled to receive the contributions your umbrella company may have made or any tax relief the Government has paid.