Legibility
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Type size by container
Containers of 237 mL or less: minimum 1 mm. Above 237 mL through 3 L: minimum 2 mm. Above 3 L: minimum 3 mm. Measured as type size, and the thresholds are volume thresholds rather than panel area ones.
Which makes 237 mL a design boundary
A 250 mL bottle takes the 2 mm minimum and a 200 mL bottle takes 1 mm. Those two sizes are adjacent on the list of standards of fill and they are not adjacent in what they demand of the label.
Characters may not be compressed
With a maximum density tied to the type size: 40 characters per inch at 1 mm, falling to 12 characters per inch at 3 mm. That closes the obvious escape route of setting the warning in a condensed face.
Contrasting background
The statement must be readily legible under ordinary conditions and on a contrasting background. Reversed out of a dark photograph, or set in a tint close to the stock, does not satisfy it.
And the label must resist removal
Labels are affixed so that they cannot be removed without thorough application of water or other solvents. A label that peels cleanly from a cold bottle with a fingernail is not meeting that.
Which is a specification for the adhesive
It has to survive refrigeration, condensation, an ice bucket and a wet bar towel, and still be hard to lift. Brief the label supplier on that requirement by name rather than describing the bottle.
Test it cold and wet
Chill the labelled bottle, put it in water, leave it, and then try to lift the label. Most adhesive failures in this craft are discovered in a bar rather than in a warehouse.
The front label fails the same way
The requirement is about labels affixed to containers of alcoholic beverages. A brand label lifting at the corner is a presentation disaster before it is anything else, and the same adhesive decision covers both.