The phrase "a strict warning" is correct and usable in written English.
It can be used when you want to emphasize the seriousness of a warning being given, often in contexts related to rules, regulations, or safety.
Example: "The company issued a strict warning to all employees about the consequences of violating safety protocols."
Alternatives: "a severe warning" or "a firm warning".
Straight Outta Compton's climax comes in Detroit when, after a strict warning, they perform Fuck Tha Police and a near riot breaks out.
It is the kind of talk that has prompted the government to treat its economic woes as a security threat, dispatching riot forces with a strict warning that anyone who takes to the streets will be dealt with harshly.
There was a strict warning not to carry more than five kilos of baggage on the little twin-prop plane from San Andrés to Providencia and I complied: what do you need on a tropical island, apart from bathers and a few T-shirts?
In a clear break with the Bush administration, the Food and Drug Administration has decided to require makers of an intravenous anti-nausea drug that had been the subject of a Supreme Court case to put a strict warning on its label.
The Zelle homepage does not at all make it clear that this is a payments service for family and friends only – it only says you can use Zelle to send money to "almost anyone you know" – language that reads more like marketing speak than a strict warning that you should, well, actually know them.
Whenever I go on vacation, my mom gives me a strict warning.
The play comes with a pretty strict warning, asking people to leave kids younger than 14 at home and cautioning would-be watchers that the "production contains flashing lights, strobe effects, loud noises, gunshots, smoking, and graphic depictions of violence and torture".
The Governor of Minnesota closed all the schools in his state, while the mayor of Indianapolis, Greg Ballard, banned driving except in emergencies – the first time the city has issued such a strict travel warning since 1978.
The committee disagreed, with most members calling for strict warning labels.
Standard cleaning materials contain toxic chemicals and strict warning labels due to their emission of off-gases that can increase indoor air pollution.
The panel did say the agency should require strict warnings on Avandia labels.
