The phrase "a strong warning in" is correct and usable in written English.
It can be used when indicating that a warning is present within a specific context or document.
Example: "The report included a strong warning in the conclusion about the potential risks of climate change."
Alternatives: "a serious caution in" or "a firm alert in".
Following a speech by Harold Wilson in which he cautioned the unions to postpone asking for more money, since bankrupt employers cannot pay wages, the Chancellor of the Exchequer, Mr. Denis Healey, delivered a stronger warning in the speech he made to the Labour Party in Leeds last Fri., forecasting that "millions" might be on the dole if militant union demands continued.
"The recent bans serve as a strong warning to everyone in the game that non-compliance with anti-doping rules carries grave consequences.
Members who identified themselves as government security agents joined the April 6 group, too, posting comments under the insignia of the Egyptian police, and as April 6 approached, the government issued a strong warning against participation in the strike.
"These bans serve as a strong warning to everyone in the game that non-compliance with anti-doping rules carries grave consequences," said Welsh Rugby Union chief executive Martyn Phillips.
A similarly strong warning in Algeria prompted an official government protest that American officials were exaggerating the threat and stirring undue fear.
The I.O.C. issued a strong warning to Athens organizers in 2000 after three years of chronic delays.
The U.S. Forest Service issued a "strong warning" about avalanche dangers in Colorado's high country due to weak snowpack and strong winds.
In a strong warning to his party, he said: "I personally think it is unthinkable to leave the European convention on human rights.
In issuing a strong warning, Andrew L. Stern, president of the Service Employees International Union, said that President Bush and Congress "have not done enough to protect and care for health care workers, their families, and patients" who could be harmed by the vaccine.
