If there is an inspection and you are found to be without legal residence, the inspectors are obliged to pass you name on to the police and immigration services. You then risk being ordered to leave the country, being admitted to a detention centre, being deported and banned from entering the European Union.
At present, there is a policy of tolerance. This means that organisations who have volunteers with no legal residence are not being prosecuted. There is no guarantee of this, of course. This policy of tolerance may be revoked at any time and the organisation may still be prosecuted.
If you do work as a volunteer for an organisation, all valid legislation applying to volunteers applies to you too. You must be given an information note, you need insurance, etc.
Voluntary work without a subordinate relationship
Legally, a person without legal residence is permitted to carry out voluntary work as long as there is no ‘subordinate relationship’. This means there is no-one telling the volunteer what they have to do.
However, we have not been able to any voluntary work whatsoever find any voluntary work where there is no discussion about whether or not there is a ‘subordinate relationship’. So legally, this condition may be met, but in practice it is unclear, or at the least uncertain, what might be included in this kind of voluntary work.