Atlanta (CNN) Some Democratic presidential candidates are not happy with the Democratic National Committee, and their anger is no longer being kept private.

At least three candidates and their closest advisers are publicly criticizing the committee, with some lambasting it for limiting space in the first two debates -- which require candidates to meet donor or polling thresholds -- and others refusing to focus a debate on climate change.

The uptick in criticism for the DNC brings to light conversations that have to date largely happened behind the scenes. But with the first Democratic primary debate in three weeks and the prospect that at least one current Democratic office holder could not make the debate stage, campaigns are starting to go public with their complaints against the DNC and their debate rules.

The DNC announced earlier this year that candidates will qualify for the first two Democratic debates -- one in June and one in July -- by achieving at least 1% support in three polls from an approved list of pollsters or receiving campaign contributions from 65,000 unique donors, including 200 donors each from 20 different states. The committee recently announced that they were doubling those thresholds for the third and fourth debates -- in September and October respectively -- requiring candidates to achieve both 2% in four polls from a slightly changed list of approved pollsters and 130,000 unique donors from the date of their campaign's creation.

Democratic National Committee Chairman Tom Perez is largely unmoved by these complaints.

In an interview with CNN Thursday here in Atlanta, Perez subtly knocked the candidates who have yet to meet the grassroots fundraising threshold and are publicly complaining.

"I think everybody has to be proficient," he said when asked about complaints about the threshold. "If you want to be President of the United States, you have to develop a proficiency at grassroots fundraising."

The three candidates at risk of missing the debates are Miramar, Florida, Mayor Wayne Messam, whose campaign has struggled to get any traction; Rep. Seth Moulton, who announced his campaign in late April and has yet to qualify on either threshold, and Montana Gov. Steve Bullock, who has currently not qualified for the debates by either committee standard and whose team is the angriest about the possible snub.

Bullock got into the race in mid-May, relatively late compared to other 2020 contenders. The governor has told CNN that he launched late because, as the governor of Montana, he had to oversee his state's legislative session, which happens every two years. Bullock did that and the body passed Medicaid expansion. His advisers now believe that the DNC rules are punishing a candidate who stayed at work instead of running for President.

"The DNC seems, on paper, interested in a 50-state strategy, but they're punishing the only candidate in the field to win a Trump state for doing his job," said Matt McKenna, a longtime Democratic operative who is advising the Bullock campaign. "I can say with 100% certainty that if Gov. Bullock announces in January, to chase after the DNC's arbitrary and secret rules, there's no way he gets Medicaid expansion though a 60% Republican legislature."

Asked about the grassroots fundraising threshold, McKenna added: "I'd say that punishes candidates from the parts of the country you fly over to get from the DNC HQ to Los Angeles."

One of Bullock's primary complaints is that a February poll from The Washington Post/ABC News is now being counted under DNC rules because it asked an open-ended question that included a host of names like Oprah Winfrey and Michelle Obama.

Bullock's campaign emailed reporters on Thursday about the poll not being allowed, calling it a "secret rule change for debate qualification."

"While Governor Bullock was expanding Medicaid to one in ten Montanans despite a nearly 60% Republican legislature, the DNC was making arbitrary rules behind closed doors," said Jenn Ridder, Bullock's campaign manager. "The DNC's unmasking of this rule unfairly singles out the only Democratic candidate who won a Trump state — and penalizes him for doing his job."

But Xochitl Hinojosa, a spokeswoman for the DNC, said Thursday that the committee "notified the Bullock campaign several times beginning in March that this poll would not count because it was open-ended and not a traditional horse race question."

The criticism from Bullock's team echo New York Sen. Kirsten Gillibrand's denunciation of the DNC's rules in an interview with CNN in May.

Gillibrand called the 65,000-donor threshold an "odd measurable" that is "random and inaccurate." Although she added, "They're the DNC, so I'll follow the rules that are given and I'll have to play by the rules," the senator said the measure "is not determinative of any of the things that matter about whether I'd beat Trump."

"Because if Madonna was running, she'd have a million supporters. She'd have more than anybody," Gillibrand concluded. "What having followers is a measurable of is whether you're famous, it's a measure of whether people know enough about you to send you a dollar."

Almost a month later, Gillibrand still remains short of the 65,000-donor threshold (she qualified based on polls months ago). She announced on Thursday that she was within 5,000 donors and her campaign spokeswoman said they had seen a recent uptick in support, days before the DNC determines who makes the first debate stage.

The one candidate who is not antagonistic of the DNC despite finding himself on the verge of missing the first debate is Moulton, who has publicly admitted he is likely to miss the event.

"No, I'm not going to make the first debate, but I knew that getting in so late," the congressman told conservative radio host Hugh Hewitt in an interview this week. "But I think that's OK, that there's, this first debate's going to have 20 people. Folks are barely going to get a chance to speak. This is a long campaign. And it's not going to be decided by the Democratic National Committee in their debates. It's going to get decided by the American people. And that's where the response to my campaign has been so positive so far."

Perez said Thursday that he has tried to have the committee be as open as possible throughout the debate negotiations. Perez said that the DNC put out the thresholds for the first two debates in February and heard back from a number of campaigns who said it was a tall mountain to climb in a short time.

"We wanted to make sure that that threshold for grassroots fundraising wasn't a lay-up, but it wasn't a half-court shot," Perez said. "And the fact that so many people have met it, what that means is more people have connected with the grassroots. You cannot win the presidency without engaging in the grassroots."

The other area of complaints stems from the fact that the DNC has declined to focus an entire debate on climate change, something that Washington Gov. Jay Inslee has asked from the committee.

Inslee sent a letter to Perez on Tuesday asking for a debate focused solely on climate change, the issue the 2020 candidate is staking his entire campaign on. By Wednesday, the DNC had already told Inslee no and warned him about attending debates outside the DNC structure that may be focused solely on climate.

Inslee seized on the moment -- and has been fundraising on it ever since.

"This is deeply disappointing," Inslee said Thursday. "The DNC is silencing the voices of Democratic activists, many of our progressive partner organizations, and nearly half of the Democratic presidential field, who want to debate the existential crisis of our time. Democratic voters say that climate change is their top issue; the Democratic National Committee must listen to the grassroots of the party."

A recent CNN poll found that 82% of Democrats or Democratic-leaning independents find climate change to be a "very important" issue, ranking it at the top of the list ahead of universal health care, tighter gun laws and impeaching Trump.

Inslee has looked to garner more support for a climate debate by calling on his competitors to support his cause. The likelihood that happens, however, is slim.

"Today, I am calling on my fellow presidential candidates to urge the DNC to reconsider its position on a climate debate." Inslee said. "Together, we can speak to the DNC with a loud voice: We need a full-length debate on the climate crisis."