(CNN) Investigators in Fulton County District Attorney Fani Willis' office have grown frustrated with the level of cooperation they are receiving from staffers in the Georgia Secretary of State's office regarding a probe into former President Donald Trump's efforts to influence the 2020 election, according to a source familiar with the criminal investigation.
The recent lack of cooperation has prompted the office to consider whether it rises to obstruction and to use subpoenas to force Secretary of State staff members to testify and share information, according to the source.
Ryan Germany, general counsel for Georgia Secretary of State Brad Raffensperger's office, disputed the notion that the office was not cooperating.
"I told the DA's office that we are perfectly willing to cooperate with reasonable requests regarding their investigation," Germany said in a statement to CNN. "I requested time to get an attorney lined up to represent our office to make sure those interactions are efficient and not disruptive. The DA's office told me that was fine."
Germany claimed the office was using anonymous sources to misrepresent their conversations, criticized that as "wildly unprofessional" and said it is "making me rethink whether we should cooperate with them."
Raffensperger on Saturday told CNN's Jim Acosta that "we're fully cooperating with the district attorney," and added that it was "false" that his office was not cooperating.
A source familiar with the Georgia Secretary of State's office told CNN that the district attorney filed an open records request Tuesday and their office is working with the investigators to fulfill that request.
The Fulton County District Attorney's Office is expected to start issuing its first round of subpoenas as early as May, and the subpoenas could be more extensive than previously expected because they are having "difficulty" getting information out of Raffensperger's office, the person familiar with the investigation said.
District Attorney Willis declined to comment on the investigation.
In a letter sent in February to numerous Georgia state election officials, including Raffensperger, Willis requested that they preserve documents related to Trump's phone call in January in which he pushed Raffensperger to "find" votes to reverse his election loss.
The investigation came as Raffensperger's office had launched its own probe into Trump's attempts to overturn the election, an inquiry that includes a review of both that call and another phone call the then-President made to a Georgia election official.
Willis said her "investigation includes, but is not limited to, potential violations of Georgia election law prohibiting the solicitation of election fraud, the making of false statements to state and local government bodies, conspiracy, racketeering, violation of oath of office, and any involvement in violence of threats related to the election's administration."
"This matter is of high priority, and I am confident that as fellow law enforcement officers sworn to uphold the Constitution of the United States and Georgia, our acquisition of information and evidence of potential crimes via interviews, documents, videos and electronic records will be cooperative," the letter reads.
Trump himself is not named in the letter, but Willis' office confirmed to CNN that the probe concerns his phone call with Raffensperger. The letter also says Fulton County authorities currently "have no reason to believe that any Georgia official is a target" in the probe.
CORRECTION: An earlier version of this article mischaracterized part of a statement from Ryan Germany, general counsel for Georgia Secretary of State Brad Raffensperger's office.
This story has been updated to add comments from Raffensperger.