I tend to not use the word ‘the’ in front of acronyms, but I see this used in documents more and more.
REIP provides regional outreach services to Northeastern Ontario.
or
The REIP provides regional outreach services to Northeastern Ontario.
If the word ‘program’ is added after REIP, I would use ‘the.’
Which is correct?
In my experience, this comes down to the difference between acronyms and initialisms. Acronyms are pronounced as a words, while initialisms have each of their letters pronounced individually.
I would expect to hear the FBI, because FBI is an initialism (aloud: "eff-bee-eye"). Whenever its full form (Federal Bureau of Investigation) is normally preceded by "the," I would expect its initialized form to be as well. For organizations that do not normally have a leading "the," I probably would not expect one for its initialized form, either, but I cannot think of an example.
I would not expect to hear the NATO, even when I would expect to hear the full form as "the North Atlantic Treaty Organization", because NATO is an acronym (aloud: "nay-toh", not "enn-ay-tee-oh").
Of course, I would expect the NATO member when NATO is used an adjective to describe the member of NATO.
I have never heard a formal rule for this.
Acronyms are abbreviations that are pronounced as words. Examples:
When using an acronym as a noun, should not put an article before the abbreviation.
On the other hand, when you are using the acronym as an adjective, you then add “the.”
As other answerers have observed, acronyms (like UNESCO) generally do not take a definite article and initialisms (like UNHCR) generally do. However, there are a number of exceptions to this rule—especially instances where initialisms appear without a definite article.
Some of the exceptions fall into recognizable categories. For example:
U.S. broadcast networks: ABC, CBS, CNN, NBC, NPR, PBS.
Corporations: AMC, AT&T, BMW, EMI, GE, GMC, IBM, PG&E, RCA, UPS
Airports whose ID codes are actual initialisms: BWI, DFW, JFK, MSP, SAT, SJC
Time zones: CST, EST, GMT, PDT
Government programs: AFDC, SDI
Common noun phrases: DNA, ESL, ESP, GAAP, HIV, HR, LPG, LSD, OCR, OJ, PR, PT, RNA, TKO
As site participant James points out in an astute comment, another category of exceptions to the "the [initialism]" rule involves abbreviated university names:
ASU, IUPUI, MSU, SMU, TCU, UCLA, USC, UT, UW
Although acronyms that normally take a definite object are much rarer, they do exist. One example is "the NASDAQ" (referring to the composite index of a U.S. stock exchange whose acronym is NASDAQ); another is "the OGPU" (a Soviet-era predecessor to Russia's FSB and SVR).
None of this is to say that the general rule that acronyms generally appear without "the" and that most initialisms—at least of proper names—are preceded by "the" is bogus. But the rule is not universally applicable, so it's wise to see how other people tend to express a particular initialism/acronym to confirm whether it follows the rule or stands as an exception to it.
