Is it permissible to sit on a chair that has been stepped on with shoes?

Treading on a chair or other object with shoes does not render it impure unless there is impurity on the shoe and it transfers to the chair. Otherwise, there is no harm in sitting on it. Avoiding a clean chair or mattress that has been trodden upon with shoes is considered an excessive strictness (tanattu'), but it is a matter of good taste to avoid treading on a mattress intended for sitting with shoes.