Which reform measure could voters use if they wanted to change a law about taxes?

The reform measure that voters could use if they wanted to change a law about taxes would be an "initiative", since this is usually used to change or alter laws that are already in place.

An initiative

Explanation:

The citizen has many ways of participating in politics, one of them is the initiative which is a way that any citizen or organization can gather several signatures to qualify a measure to be placed on a ballot and be voted upon in future election. The Initiatives can be divided into many types, such as constitutional amendments and statutory initiatives.

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