The correct answer is: article not required.
A union leader is a person who is elected or appointed to represent the interests of the members of a union. They are responsible for negotiating with management on behalf of the union members, and for representing the union in court or other legal proceedings.
The article “a” is used before singular nouns that refer to a general or unspecified person or thing. In this case, the noun “union leader” is not being used in a general or unspecified way. The speaker is referring to a specific union leader, so the article “a” is not necessary.
The article “an” is used before singular nouns that begin with a vowel sound. In this case, the noun “union leader” does not begin with a vowel sound, so the article “an” is not necessary.
The article “the” is used before singular nouns that refer to a specific person or thing. In this case, the noun “union leader” is not being used in a specific way. The speaker is not referring to a specific union leader, so the article “the” is not necessary.
Therefore, the correct answer is: article not required.