Non-native English speakers often find it difficult to know when to use “a”, “the” or no article with initials and acronyms.
The key is to know what the initials mean. If the initials are a proper noun (name), then you should not use an article (this follows the rule concerning article use with names). If the initials are descriptive, then you will probably need to use either “the” or “a”.
For example, company names do not usually require an article, e.g.: BMW (Bayerische Motoren Werke), GE (General Electric), GM (General Motors), LG (Lucky Goldstar), CNN (Cable News Network). Neither do initials describing people, e.g. JFK (John Fitzgerald Kennedy).
But if the initials are a description of e.g. countries, authorities or organisations, you should use “the”, e.g.: the USA, the UK, the UN, the CIA (Central Intelligence Agency), the FBI (Federal Bureau of Investigation), the EU (European Union), the ECJ (European Court of Justice), the OSCE (Organization for Security and Cooperation in Europe)
An exception here is the BBC, which we say even though the BBC is a company. “BBC” stands for “British Broadcasting Corporation”, so the name acts like a description of a corporation. General Electric is a corporation too, so we could equally as well say the GE corporation, but according to convention, we just refer to it by name – GE.
Acronyms are pronounceable names made up of a series of initials. Thus, as proper nouns, they do not need an article. E.g. NATO, NASA, UNESCO, OPEC, VAT
“A” or “an”?
Although we write a limited liability company, we write an LLC.
The choice of “a” or “an” is determined by the pronunciation of the initials (LLC is pronounced el-el-see, so, as it starts with a vowel sound, we must use “an”).
Other examples: a marketing authorisation holder becomes an MAH, a special purpose vehicle becomes an SPV
As acronyms are pronounced as words, we say, e.g. a NATO resolution, an OPEC member