'working fiercely' is a perfectly correct and usable phrase in written English.
For example, "John worked fiercely on his project, burning the midnight oil until it was completed."
Mr. Boehner's willingness, however reluctant, to support a Democratic bill gives him an aura of flexibility after two years of working fiercely to block Mr. Obama's agenda.
In conversation with some very high-ranking AI execs at Intel -- which is also working fiercely competitively in this space, with multiple solutions from FPGAs to its Nervana Neural Network processors -- this obstacle of scalability is paramount.
With the same bill stalled in the House, Republicans are working fiercely to fast-track SB 529 through the Senate with the hopes of restricting the rights of African-American women by name and all women by intent.
Since the early 90s' Yoncé -- or Sasha in 2008 -- has been working fiercely at her craft, which has consisted of all-nighters, nervousness, last minute changes, frustrations, transcontinental flights at wee hours of the morning, severe jet lag and probably a bunch of other things that artists experience on the journey to stardom.
Above all, they are lovable for the sake of Gluckel herself: hard working, fiercely devoted to her numerous family, valuing social position but also financial integrity, caught between her natural assertiveness and her determination to be humble before God.
"On the contrary, it reinforces ideas we've worked fiercely at challenging and moving beyond from.
After the stroke, he lost almost all his language, but he worked fiercely for twelve hours a day to get it back.
He worked fiercely to protect author's rights and interests, and served on the executive board of the Society of Authors Representativess for more than 20 years.
This was especially true early in his career, when he worked fiercely to dissolve, or at least to challenge, traditional social categories like race, gender, and sexuality.
The director, Glendyn Ivin, and the show's writers (Chayko, Matt Cameron and Phil Enchelmaier) work fiercely to establish themselves as dramatists and not polemicists, and to chew on complex, meaty ideas and investigate ethical grey areas.
Paul has worked fiercely to reinvent himself and his family, and the new Sabine collection represents the reinvention of France after the stain of Nazi occupation and collaboration in World War II".
