Dropping the article before government agency abbreviations?

I live in Washington DC and work for a government contractor. In conversation, people often drop the "the" before the acronym of a federal agency. For example, someone might say "I heard FDA is considering a new rule" instead of "I heard the FDA is considering a new rule." Is this proper English or Beltway slang?

I've found official sources dropping the "the." Here are two examples from the Supreme Court:

"...pursuant to FDA's comprehensive safety and efficacy authority under the Federal Food, Drug, and Cosmetic Act..." (PDF source)

Despite the obvious implications for many employers of deep religious conviction, HHS decided to exempt only some nonprofit religious employers from compliance (PDF source).

But people often include the definitive article. Again from the Supreme Court:

And the FDA ultimately ordered Merck to add a warning about atypical femoral fractures... (PDF source)

Is there a rule for when the definitive article is necessary? I found two previous SE questions (here and here) but neither addresses my question.

Omitting the article is Beltway slang. Within organizations it is common to strip articles from initialisms that would otherwise bear them. A decade ago, John McIntyre of the Baltimore Sun noted that Washington bureaucrats commonly omit the:

The definite article is used before abbreviations of agencies — the FBI, the CIA — and nations — the U.S., the U.K. — but not before the abbreviations of universities' names. Devoutly as some might wish, Ohio State University is not called the OSU. Some bureaucrats indulge in omitting the article before the names of their agencies, because they are very important people, pressed for time on the nation's business and too urgently focused on the public weal to trifle with the definite article. For them, it's OMB says and EPA reports. But if you were interested in mimicking pomposity, you wouldn't be reading this.

As for what you should do, that is largely a question of usage. You can refer to your favorite style guide if you want a rule.

For example, the Chicago Manual of Style (10.9) defers to established usage, and suggests that, in the absence of established use, the should be kept:

Initialisms, which are read as a series of letters, are often preceded by a definite article (“member nations of the EU”). Whether to include the article may depend on established usage. For example, one would refer to the NBA and the NAACP, on the one hand, but to W3C, PBS, and NATO, on the other—though all these organizations include the definite article in spelled-out form. If no established usage can be determined, use the definite article if it would be used with the spelled-out form.

Otherwise, you can conform to your audience's expectations, where there is no hard-and-fast rule. If this is an internal report, and you don't have an internal style guide saying one way or the other, omitting the article may be fine. If this is a public-facing document, using the article may be more likely.