The phrase "adamant opponents" is correct and usable in written English.
It can be used to describe individuals or groups who are firmly and resolutely opposed to something.
Example: "The environmentalists were adamant opponents of the proposed oil drilling project, arguing it would harm the local ecosystem."
Alternatives: "staunch adversaries" or "unyielding critics".
German business groups have been among the most adamant opponents of sanctions.
Evangelistic churches, often among the most adamant opponents of same-sex marriage, are especially rare, and Catholicism is waning.
Mr. Ashcroft has been one of the Senate's most adamant opponents of a woman's right to choose an abortion.
Opponents objected that the law "inflicted a grievous wound on the Constitution" — it "subverts and changes our Form of Government" and "silences and stifles the voice of the Majority". The machinations of Henry and Gerry, adamant opponents of the Constitution, hardly embodied its spirit.
"The real adamant opponents of nuclear weapons argue that they've never had any use whatsoever," he says, "that they didn't help to end the second world war, that they didn't prevent the Soviets from overrunning Europe, and I don't agree with that.
Attorney General Jeff Sessions is among the most adamant opponents of marijuana in the country.
He is perhaps best remembered as an early and adamant opponent of the Vietnam War.
Richard Nixon, whose administration was attempting to deport Lennon, a vocal and adamant opponent of the Vietnam War.
And just maybe, the changed climate may hasten the return of Sidney Crosby, who understandably is an adamant opponent of all head shots.
Earning a reputation as a highly competent administrator, he was appointed to the premiership and to other key positions in 1826 and remained an adamant opponent of reform for the next two decades.
In this role reversal, the most adamant opponent of pump-priming has turned out to be Chancellor Gerhard Schröder in Germany, who controls a center-left government consisting of the Social Democratic Party and the Green Party.
