Given the task definition and input, reply with output. This task is about reading the given passage and construct a question about the information present in the passage. Construct a question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) its answer is a continuous text span from the paragraph. Avoid creating questions that (i) can be answered correctly without actually understanding the paragraph and (ii) uses same words or phrases given in the passage.

On 23 October 1501, at Mielnik Polish–Lithuanian union was reformed at the Union of Mielnik (Polish: unia mielnicka, unia piotrkowsko-mielnicka). It was there that the tradition of the coronation Sejm (Polish: "Sejm koronacyjny") was founded. Once again the middle nobility (middle in wealth, not in rank) attempted to reduce the power of the magnates with a law that made them impeachable before the Senate for malfeasance. However the Act of Mielno (Polish: Przywilej mielnicki) of 25 October did more to strengthen the magnate dominated Senate of Poland then the lesser nobility. The nobles were given the right to disobey the King or his representatives—in the Latin, "non praestanda oboedientia"—and to form confederations, an armed rebellion against the king or state officers if the nobles thought that the law or their legitimate privileges were being infringed.
When did the Mielnik Polish–Lithuanian union reform?