Every time Arizona state Rep. Juan Mendez (D) shows up for work at the state Capitol, he can expect someone to ask him to seek the help of a higher power. Each session of the state House of Representatives is required to begin with a prayer -- almost always Christian in nature -- and while that doesn't mesh with Mendez's views as an atheist, he's come to accept that it's an important tradition for many of his colleagues. Members of the House can sign up to lead the morning prayer, and Mendez himself has things he'd like to say -- things about science and nature and humanity. But for years, he says, he's been denied the chance to lead the invocation out of concern that he wouldn't mention God in his remarks.

On Thursday, Mendez was finally able to deliver his own version of a prayer when a colleague offered up his slot. Mendez's remarks held true to his values as a nonbeliever, which in turn angered his Republican colleagues and put the hotly contested issue of separation of church and state back in the spotlight.

During his invocation, Mendez expressed gratitude for the "pluralistic society" he represented, as well as the "beauty of our multicultural state that reflects our diversity of color, of heritage, of religion and lack thereof."

He encouraged lawmakers to "accept each other for our differences" and suggested that religious faith isn't necessarily a prerequisite for having a moral compass.

"We need not tomorrow's promise of reward to do good deeds today," Mendez said in his invocation. "For [while] some may seek the assistance of a higher power with hands in the air, there are those of us that are prepared to assist directly, with our hands to the earth. Take these words to heart as we move this great state of Arizona forward. It is our responsibility to honor the Constitution and the secular equality it brings. And so shall it be."

For House Majority Leader Steve Montenegro (R), a Christian minister, those words didn't suffice. Montenegro has taken the position that all prayers must include a reference to a higher power -- which Mendez's didn't. Almost as soon as Mendez finished speaking, Montenegro called upon the Rev. Mark Mucklow to fulfill that criterion.

"At least let one voice today say thank you," Mucklow told the chamber. "God bless you and bless your families for the time you sacrifice and are away from them down here late at night. Father give back to them that time. Multiply it back to them and give them harmony and peace in their families. Father may they draw close to you and Father may we all be grateful for the work they do today. In Jesus' name we pray. Amen."

With that, Montenegro declared that official business could begin. And when it did, a number of Republicans made it clear that they saw Mendez's behavior as nothing less than an attack on their faith.

"I'm saddened and offended that a member of this body would knowingly disregard our call for prayer and our House rules," said state Rep. Mark Finchem (R), according to Capitol Media Services' Howard Fischer.

Finchem went on to argue that the "republican form of government came out of the Book of Exodus" -- a questionable claim -- and said prayer was needed for the purpose of "lifting this body up" to God.

State Rep. Kelly Townsend (R) was similarly upset, saying she "took offense at some of" Mendez's words.

"It's not time to be proselytizing even if you're proselytizing something that's not a religion," she said, according to Fischer.

"We need not tomorrow's promise of reward to do good deeds today." Arizona state Rep. Juan Mendez (D).

It's not clear which part of Mendez's invocation could be considered "proselytizing" -- at least any more so than Mucklow's -- but in any case, such behavior would be illegal under Town of Greece v. Galloway, the most recent Supreme Court case on the issue of church/state separation. In their 2014 ruling, the justices held that religious prayer in government meetings is constitutional as long as there is a policy of nondiscrimination and as long as the invocations don't proselytize or denigrate against people of any faith, or lack thereof.

Groups like the Freedom From Religion Foundation, a nonprofit dedicated to defending the separation of church and state, say these protections apply to nonbelievers as well.

Andrew Seidel, an attorney for the FFRF, said that putting a halt to government prayer would be the most obvious way to avoid controversies like this. Until then, he believes government must respect the diversity of people's religious views, or lack thereof, in the public sphere.

"In a pluralistic society like ours, when the government opens the door to religion, officials should expect to hear messages they don't like," Seidel told The Huffington Post in an email. "Government officials are free to pray at any time, before, during, or after their meetings. But that is not enough for some. Some need to be seen praying. They want to use religion to pander and, in the process, they denigrate themselves, their office, their community, and their religion."

Zenaido Quintana, chair and acting director of the Secular Coalition for Arizona, maintained that Mendez's invocation fell within the boundaries laid down by the Supreme Court. But he also raised concerns about what he sees as persistent discrimination against Mendez over his outspoken atheism.

"It certainly violates the spirit of Greece v. Galloway, that you not discriminate against minority religions," he said. "That you'd have a number of lawmakers jump on Rep. Mendez in an effort to kind of intimidate him or embarrass him."

Quintana said that response from Mendez's fellow lawmakers suggests the whole thing may have been a "bit of a setup."

"Montenegro had his minister standing by to provide an invocation within his criteria," he said. "Then he systematically had several of Mendez's fellow legislators effectively criticize him on the floor for speaking his truth."

Stephanie Grisham, a spokeswoman for Montenegro, told HuffPost the majority leader interprets Greece v. Galloway as only protecting the right to deliver an invocation that's religious in nature.

"Prayer is prayer," she said.

Grisham said a chaplain is present at every Arizona House session, and that the other lawmakers who objected to Mendez's remarks Thursday did so of their own volition.

Mendez did not respond to a request for comment.

Quintana said he believes Mendez's public dressing-down is a symptom of a widespread disrespect in the state legislature for religiously unaffiliated people -- a population that's growing nationwide.

"We are a very diverse state, and increasingly so, and the diverse elements in these kinds of beliefs are getting more and more disparate," he said. "There's lots of them, and they're also getting more and more vocal. There's real unhappiness arising from this, and we just need to make sure that our elected representatives are aware of it."