I recently looked up my employer on the ICO site as to what data that are registered as being able to use and share. Website here: https://ico.org.uk/esdwebpages/search There are a number of things that I have noticed that I am wary of in bold, below: Nature of work - General business Description of processing The following is a broad description of the way this organisation/data controller processes personal information. To understand how your own personal information is processed you may need to refer to any personal communications you have received, check any privacy notices the organisation has provided or contact the organisation to ask about your personal circumstances. Reasons/purposes for processing information We process personal information to enable us to promote our goods and services, to maintain our accounts and records and to support and manage our staff. Type/classes of information processed We process information relevant to the above reasons/purposes. This may include: personal details family, lifestyle and social circumstances financial details employment and education details goods or services provided We also process sensitive classes of information that may include: physical or mental health details racial or ethnic origin religious or other beliefs of a similar nature trade union membership Who the information is processed about We process personal information about our: employees customers and clients suppliers and services providers advisers, consultants and other professional experts complainants and enquirers Who the information may be shared with We sometimes need to share the personal information we process with the individual themself and also with other organisations. Where this is necessary we are required to comply with all aspects of the Data Protection Act (DPA). What follows is a description of the types of organisations we may need to share some of the personal information we process with for one or more reasons. Where necessary or required we share information with: family, associates and representatives of the person whose personal data we are processing employment and recruitment agencies current, past and prospective employers educators and examining bodies central government credit reference agencies suppliers and service providers debt collection and tracing agencies financial organisations Transfers It may sometimes be necessary to transfer personal information overseas. When this is needed information is only shared within the European Economic Area (EEA). Any transfers made will be in full compliance with all aspects of the data protection act. Statement of exempt processing: This data controller also processes personal data which is exempt from notification Am I being paranoid here or does that say that they can / do share information about who are trade union members to prospective employers? I'm not saying it's blacklisting but........