The phrase "a firm control" is correct and usable in written English.
It can be used to describe a strong or authoritative management or oversight over a situation or subject.
Example: "The manager maintained a firm control over the project's budget and timeline, ensuring everything stayed on track."
Alternatives: "a strong grip" or "a tight hold".
Mackerras stayed in the post until 1977, exercised a firm control on the style and content of productions and was instrumental in broadening the repertory.
Shahu has a firm control over the excited posse who follow him in the hope of becoming "one of the biggest drug dealing gangs of the town".
David DiMartino, a spokesman for the Democratic Senate Campaign Committee, said: "The difference this time is that Governor Nelson has a firm control over the campaign, which is staffed by some of the best political professionals in Nebraska.
[ 5 ] In each of our own countries, it remains essential to maintain a firm control of public spending within an appropriate medium-term framework of fiscal and monetary policies.
By streamlining and having a relentless focus on ease of use, elegance and a firm control on the lines of production, Jobs absorbed the lesson of so many successful models: less is always slightly more.
During World War II the French colonial regime exercised a firm control over Bao Dai until the Japanese coup de force of March 1945, which swept away French administration in Indochina.
A firm controlled by Romain Zalesky, a French financier, gets 20% in return for its 10.3% stake in Montedison.
1033, 1037, 12 L.Ed.2d 1964964) (Harlan, J., dissenting), concludes that the merger 'produces a firm controlling an undue percentage share of the relevant market,' ante, at 366.
It filed for bankruptcy just weeks later after disclosing that a $430 million debt owed to the company by a firm controlled by Mr. Bennett had been concealed.
A firm controlled by Mr. Ross bid $435 million yesterday to buy the service unit of American Home Mortgage, which collects payments from homeowners.
