Mandatory Reconsideration is challenging a benefit or tax credit decision when you disagree with the outcome.
You normally have to ask for a Mandatory Reconsideration within one month of the decision date (the date on the decision letter) if you are challenging a benefit decision. If you are challenging a Tax Credits decision the deadline is 30 days.
You can appeal to an independent tribunal after you receive a Mandatory Reconsideration Notice. However with Housing Benefit and Council Tax Support decisions you can go straight to appeal without having to ask for a mandatory reconsideration.