Denver International Airport began tests on their enormous, flashy-new welcome sign to the Mile High City on Tuesday.

There's a catch, though, and you can blame it on an obscure federal rule.

Now, if the airport wants to make money off of the sign that’s going to be 1,000 feet long, 16 feet tall and made of LED lights, it will need a literal Act of Congress.

The 900 light poles being strung up on Pena Boulevard should be operational by the end of October – but, a federal highway rule that the airport didn’t know about is limiting them to uses on-premises ads only.

So, they can’t sell big money “Welcome to Denver” messages from events and corporations.

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And, no offense to airport retailers like Climax Jerky, Rebel Popcorn and Kazoo n’ Company Toy Store, but their budgets won’t pay for the sign, meaning the airport will get stuck with that whole $14.5 million bill up front.

They’d originally planned to split the cost with Panasonic in exchanging for also splitting ad revenue.

Unfortunately though, Panasonic split when the ad plans ran into trouble.

RELATED: Next Question: WIll proposed DIA sign follow federal law on outdoor advertising?

The airport is asking Congress to fix the issue and also appealing to the Trump administration.

But until the can get help from Congress, there are only so many messages DIA can legally put on its welcome sign.