The phrase "a firmer message to" is correct and usable in written English.
It can be used when you want to convey a stronger or more assertive communication directed towards someone or a group.
Example: "The manager decided to send a firmer message to the team about meeting deadlines."
Alternatives: "a stronger message to" or "a more assertive message to".
More than the money, it is reputed to want to send a firm message to the world's resource nationalists.
Fortunately, President Bush sent a firm message to troublesome Turks: "We expect them not to go into northern Iraq".
In the middle of it all, Steinbrenner's hand-picked captain, Derek Jeter, gave a firm message to his teammates.
If the royal family wish to send out a firm message to the press they can look to Ireland, where the photographs have also been published.
At some point perhaps there will be enough of us to send a firm message to our elected officials in Trenton that enough is enough.
Mr. Kerry, in his television appearances, said that if Congress passed a measure authorizing the use of force, it would send a firm message to Iran that the United States would not tolerate the fielding of a nuclear device, and thus safeguard Israel's security.
By reaching the final of the ATP World Tour Finals he reclaimed third place from Andy Murray; by beating Jo-Wilfried Tsonga in three tough sets last night to win a record sixth title, he sent a firm message to Djokovic, Rafael Nadal, Murray and all the rest that, at 30, his hunger for success has not diminished.
The Falkland Islands government decided to counter Argentine claims by scheduling a referendum on the status of the islands, saying that it wanted to "send a firm message to Argentina that the islanders want to remain British".
The move was meant to send a firm message to Assad, and at the time, Trump said it was in the "vital national security interest of the United States to prevent and deter the spread and use of deadly chemical weapons".
BBC news director Helen Boaden returned to work on Thursday — one day after the release of the Pollard report, which blasted the network's management for its handling of the Jimmy Savile investigation — with a firm message to staffers.
