Under Articles 29 & 31 of Commission Decision C(2018) 5119, with the catchy title of Commission Decision on the internal procedure provisions for the recovery of amounts receivable arising from direct management and the recovery of fines, lump sums and penalty payments under the Treaties, the fine amount (plus interest) can be recovered through deductions from EU payments due to the member state.
Recovery procedure and default interest applicable
- If the Member State upon which the Court of Justice has imposed a lump sum or penalty payment has not effected
payment by the deadline specified in the letter requesting
payment, the accounting officer shall immediately send a letter of
formal notice, asking it to pay the amount owed within
fifteen calendar days, plus default interest at the rate referred
to in Article 9.
- If payment has still not been made on
expiry of the fifteen calendar days following receipt of the
letter of formal notice by the Member State, the accounting
officer shall recover the amount by offsetting in accordance
with the procedure set out in Article 31 after having informed
the authorising officer responsible and having given the indebted
Member State the opportunity to submit comments.
In the circumstances provided for in
Article 29(2), the total amount of the lump sum or penalty
payment imposed by the Court of Justice, plus interest, shall
be deducted from payments due to the Member State.
In this specific case of the Turów coal mine, this procedure was alluded to by a European Commission spokesperson quoted by Polish news website Interia.pl (my translation):
In practice, this is done through requests for payment from the
Commission to the Member State. If the payment is not made (within the
set deadline) and after allowing the Member State to provide
explanations, the financial penalty should be recovered by deducting
from payments due to the Member State in question.