"fervent opposition" is correct and usable in written English.
You can use it in a sentence when you want to describe strong opposition to something. Example sentence: The speaker expressed her fervent opposition to the proposed policy.
Fervent opposition to abortion, which eventually cemented the alliance between conservative Protestant and Catholics, came later.
McCain and Huckabee's achievements came in the teeth of fervent opposition from supposed giants of the conservative movement.
Nigeria refuses, arguing that reforms that are too obviously foreign-imposed will arouse fervent opposition, and therefore fail.Debt relief need not be sudden or unconditional.
The fervent opposition to gun control has caught the National Sheriffs Associationn, the primary industry group for more than 3,000 sheriffs, off guard.
The most fervent opposition can be found in Sadr City, the Shiite slum in Baghdad that represents the heart of Mr. Sadr's constituency.
He started his political career in the Colorado statehouse as a member of a group called "The Crazies" because of their fervent opposition to taxes.
Representative Richard A. Gephardt of Missouri, a Democratic presidential candidate, told abortion rights supporters tonight that he had abandoned his once-fervent opposition to abortion because of "wisdom gained over time".
Quisling's attempts to convert the church, schools, and youth to National Socialism aroused fervent Norwegian opposition.
Such pragmatism may be enough to shift opinions about the wisdom of legalisation, but it rarely generates the moral passion necessary to overwhelm fervent moral opposition and bring about lasting change.
Tipping didn't take hold here until after the Civil War, and even as it spread it met with fervent public opposition from people who considered it a toxic vestige of Old World patronage.
But through a mix of compromise and calculated bullying, including the abrupt dismissal of two far-right ministers before the vote, Mr. Sharon appeared to be advancing toward his goal despite fervent rightist opposition.
