Hi all. I've been self employed now for three years, trading as a sole trader and taking care of my own tax afairs. Most of my work is private, but also some light commercial or industrial. Up until now I have never had problems with payments. However, recently I did a small job for a company of shop fitters. No problems with payment. But I have just had an email from then asking for details of my CIS card. If I don't provide them details they will deduct 30% tax from any future invoices. So excuse my ignorance for something I feel I should know is what is a CIS card? should I have one? and if so where do I get one and what does it cost, do I have to prove my qualifications to get it etc etc. Also if they DO deduct tax, why 30%? I don't earn enough to push me into the higher rate tax band, so I would be happy if they deducted just the normal 22% tax, then it would go into my accounts as tax paid, but why 30%?