Explanation:

- Bali refers to a kind of taxation or tribute paid by the citizens in ancient India. It's usually in the form of goods, grains, or money provided to the ruler or the state.

- Sulka is often related to tax or toll, again not directly linked with unpaid labor but rather a financial obligation or duty.

- Udranga is not a commonly referenced term in the context of ancient labor practices; it might relate to some form of taxation or payment under certain contexts.

- Visiti refers to the practice of unpaid labor which subjects had to provide as a form of service, often to the king or local authority.

Visiti is indeed the correct answer related to unpaid labor.