You can complain by phone, letter or online. National Minimum Wage Helpline: 0845 6000 678. Normal opening hours Monday to Friday 9am-5pm. All calls charged at local rates. Callers can be assisted in 30 different languages. Changed Christmas hours (normal hours days not stated): Monday 24 December, 9am-4pm; Tuesday 25 December, closed; Wednesday 26 December, closed; Monday 31 December, 9am-4pm; Tuesday 1 January - closed. You can also write to:National minimum Wage Enforcement Unit, BP7102, Northam House, Benton Park View, Newcastle Upon Tyne, NE98 1ZZ. Or complain online at: http://www.hmrc.gov.uk/nmw/nmw_complaint_form.pdf