The standoff between former Atlanta fire chief Kelvin Cochran and the city that used to employ him escalated on Thursday, when Cochran’s attorneys announced that they have filed a federal lawsuit.

The suit accuses the city of firing Cochran because of his religious beliefs, violating his constitutional rights.

Cochran’s case has become a focal point in a larger national debate over public religious expression protections and the civil rights of LGBT Americans.

Cochran, who is an evangelical Christian, was terminated in January after a city investigation pertaining to his self-published book, “Who Told You That You Were Naked,” a Bible study-style text that covers a range of his personal religious beliefs. In one section of the book, Cochran called “homosexuality” and “lesbianism” a “sexual perversion” morally equivalent to “pederasty” and “bestiality.”

Atlanta Mayor Kasim Reed said in January that Cochran’s firing was over his “judgment and management skills,” and that “Cochran’s personal religious beliefs are not the issue.” The city had suspended Cochran in November, after questioning whether the book’s passages on homosexuality violated the city’s non-discrimination policy.

But that is not at all how Cochran and his growing number of supporters see things.

“To actually lose my childhood-dream-come-true profession – where all of my expectations have been greatly exceeded – because of my faith is staggering,” Cochran said in a statement released with news of the lawsuit. “The very faith that led me to pursue my career has been used to take it from me.”

The complaint, provided by Cochran’s lawyers, claims: “Defendants fired Cochran solely because he holds religious beliefs concerning same-sex marriage and homosexual conduct that are contrary to the Mayor’s and the City’s views on these subjects.”

It adds: “Cochran, and other City employees who agree with Cochran’s religious views regarding same-sex marriage and homosexual conduct, are under a constant state of threat of the City taking adverse action against them — up to and including termination — if they express those views inside and outside of work.”

In an administrative federal discrimination complaint filed with the Equal Employment Opportunity Commission last month, Cochran stated: “I have been discriminated against because of my religion — Christian.”

Last week, six members of Georgia’s congressional delegation wrote a letter to Mayor Reed in support of Cochran’s reinstatement. “Your action against Chief Cochran appears to violate fundamental principles of free speech and religious freedom,” it reads. “The only way Chief Cochran could avoid his views would be to disown his religion.”

The letter, written by Rep. Barry Loudermilk (R) and co-signed by five other Republican members of Congress, adds: “Atlanta itself engaged in an act of discrimination.”

Cochran’s case has become a rallying point for several conservative religious groups that believe some laws and policies designed to protect LGBT individuals from discrimination are a violation of religious liberty protections. Those groups include the Alliance Defending Freedom, which is legally representing Cochran;  the Faith and Freedom Coalition; the Family Research Council; and the Georgia Baptist Convention.

“The idea that the government can force public servants to surrender their First Amendment rights is outrageous,” Tony Perkins, president of the Family Research Council, said at a mid-January religious freedom rally at the Georgia State Capitol, according to the Christian Post. “If a government will fire someone for their religious beliefs, no beliefs are safe from government regardless of how sacred those beliefs may be. Mayor Reed is sending a very clear message that Christians must check their faith at the door of public service.”

On its Web site, the Alliance Defending Freedom takes the position that same-sex marriage is “the most prominent and pressing danger to fundamentally altering marriage, as it undermines the good that marriage provides society” — and that “those who believe in marriage,” by which the group means those who believe in heterosexual marriage only, “are politically, culturally, and legally persecuted for those beliefs.”

Cochran’s dismissal has also hovered in the background of a pair of controversial religious liberty bills currently being considered in the Georgia legislature.

The city has the support of LGBT rights groups such as Georgia Equality and Lambda Legal, along with the Atlanta Professional Firefighters Union, which released a statement commending Reed for Cochran’s termination. “Local 134 supports LGBT rights and equality among all employees,” it reads.

Human Rights Campaign president Chad Griffin said in January that “the fact that Mayor Reed lost confidence in Kelvin Cochran’s ability to do his job is completely unsurprising, and his decision to terminate Cochran was right, fair and in the best interest of all Atlanta’s residents.

“People of faith take their religious convictions with them to the workplace every day, but Cochran’s unprofessional and irresponsible conduct was completely unrelated to his personal convictions.”

Jenna Garland, a spokeswoman for Mayor Reed, said Wednesday that the city of Atlanta would “rigorously defend” itself against Cochran’s legal actions and is “confident that the decision to terminate Mr. Cochran was both the right thing to do and fully legal.”

The city also disagreed with Cochran’s version of the story on several major points, as it has done in the past.

In the compliant and in previous statements, Cochran has said that he sought the permission of Nina Hickson, the City of Atlanta Ethics Officer, before publishing the book. He says he was told that “so long as the subject matter of the book is not the city government or fire department he could write the book.”

Garland, the mayor’s spokeswoman, countered in a lengthy January statement that “Mr. Cochran was told that the City Code required him to get the approval of the Board of Ethics before publishing his book, something he admits he never did.”

Cochran has also said, both in the complaint and in his previous administrative discrimination filing, that “the [city] investigation revealed zero instances of discrimination by me against any other employee of the city.”

“What he was actually told was that his distribution of a book about his beliefs within his department had caused his employees to question his ability to continue to lead a diverse workforce,” Garland’s January statement reads, adding that the city believes Cochran’s overall conduct before and during the investigation “reflected poor judgment and failure to follow clearly defined work protocols.”

“The City of Atlanta remains a place where all people, including those who share Mr. Cochran’s beliefs, are equally valued and respected,” Garland added on Wednesday. “However, religious beliefs cannot shield any employee from the consequences of poor judgment and insubordination.”

Both sides of the matter do agree that Cochran distributed his book to several Atlanta fire employees during his tenure.

Cochran’s complaint says that the fire chief distributed the book to “10 AFRD employees who he knew were Christians,” and who had requested copies of the book; to “approximately 3-5 additional employees who approached him and requested a copy of the book”; and to “three command level AFRD employees” who “previously shared their Christian faith with him.”

In its report on the matter, the city says that Cochran distributed the book to at least nine employees, three unsolicited.

Based on interviews with multiple city employees, the city’s report concluded that “there was a consistent sentiment among the witnesses that firefighters throughout the organization are appalled by the sentiments expressed in the book. There also is general agreement the contents of the book have eroded trust and have compromised the ability of the chief to provide leadership in the future.”

Again, Cochran disagreed. “During this time frame, Cochran’s book caused no disruption with any city practices or procedures or in the workplace at all,” the complaint argues.

In the complaint, Cochran asks for compensatory damages, reinstatement to his old job and a pair of declarations from the city stating that it violated his constitutional rights.

The complaint also asks for the city to “stop enforcing their policies…and practice of allowing adverse employment actions against Cochran and other City employees for expressing protected religious messages about marriage and sexuality when those messages are about matters of public concern.”