(CNN) The Government Accountability Office will investigate whether individuals connected to President Donald Trump's Mar-a-Lago club in Florida have had inappropriate influence over the Department of Veterans Affairs, according to a letter sent to Democratic Sen. Elizabeth Warren of Massachusetts.

The GAO's investigation comes after a ProPublica story in August raised questions about three people with ties to Mar-a-Lago, Marvel Entertainment Chairman Ike Perlmutter, Palm Beach-area doctor Bruce Moskowitz and attorney Marc Sherman -- all private citizens with no official government roles -- and whether they were affecting decisions at the department.

Several former Veterans Affairs officials and a current official told CNN in August that an informal council was exerting sweeping influence over the department from the President's Mar-a-Lago club, corroborating ProPublica's report, which said the three individuals "prodded the VA to start new programs, and officials traveled to Mar-a-Lago at taxpayer expense to hear their views."

The group of three, led by Perlmutter, was very open about the fact that they had been "anointed by the President and had his full support to influence policy at the VA" despite never being appointed or installed as formal advisers, sources told CNN at the time.

CNN reached out to Perlmutter, Moskowitz and Sherman for comment on ProPublica's report, but they have not yet responded. The three told ProPublica in a statement in August that they "offered our help and advice on a voluntary basis seeking nothing at all in return."

"While we were always willing to share our thoughts, we did not make or implement any type of policy, possess any authority over agency decisions, or direct government officials to take any actions," the statement said.

Veterans Affairs spokesman Curt Cashour, responding to CNN's request for comment in August, did not specifically address details about the three men but said in a statement that the department appreciates "hearing from experts both inside and outside VA as we look for better ways to serve our nation's heroes."

"This broad range of input from individuals both inside and outside VA has helped us immensely over the last year and a half -- a period that hands down has been VA's most productive in decades," the statement said.

Following the story, Warren and Democratic Sen. Brian Schatz of Hawaii asked the GAO to investigate the matter. The agency announced in a letter that it plans to do so in several months when it has the staff resources.

"GAO accepts your request as work that is within the scope of its authority," the GAO wrote in a letter to Warren dated November 19. "At the current time we anticipate that staff with the required skills will be available to initiate an engagement in about five months. As applicable, we will also be in contact with the cognizant Inspector General's office to ensure that we are not duplicating efforts. If an issue arises during this coordination, we will consult with you regarding its resolution."

It's not unusual for the GAO, a watchdog congressional agency, to look into issues raised by senators.

The trio's influence at the Department of Veterans Affairs caused "frustration and confusion ... for career government employees having to work outside the bounds of what we know is right," one former department official previously told CNN. "We tried on the government side to keep things appropriate, but senior VA officials were applying pressure to meet these outside demands."

The former Veterans Affairs official noted that in the summer of 2017 some in the organization had been reprimanded for openly discussing Perlmutter's involvement. Former Secretary David Shulkin was among those who told staff to keep quiet about the fact that the Marvel magnate was so closely involved in the agency under the "auspices of protecting his privacy," CNN previously reported.

In August, the liberal advocacy group VoteVets filed a lawsuit asserting the group violated "federal laws that regulate the ability of private interests to shape federal policy," which the Veterans Affairs Department sought to dismiss , arguing federal law did not apply to any alleged voluntary and informal advice of the three men.

The Veterans Affairs inspector general has declined lawmakers' requests for an investigation while a private lawsuit on the issue is pending.

But the GAO has agreed to take on the investigation, which comes as Democrats plan to turn up the heat on their investigations into the Trump administration with their new House majority in January. Democrats on the House Veterans' Affairs Committee have already made it clear that the issue is among those they plan to look into.

The committee's ranking member, Democratic Rep. Tim Walz of Minnesota, has been asking for answers about the issue since August. On August 8, he asked Veterans Affairs Secretary Robert Wilkie to give the committee "any and all communications between VA officials and "Ike Perlmutter, Bruce Moskowitz, and Marc Sherman as well as travel records to and from Mar-a-Lago."

In October, Walz once again sent a letter demanding answers and accusing the VA of stonewalling on the issue.

"VA's refusal to cooperate with this inquiry is absolutely unacceptable," Walz said. "When the story of VA shadow rulers at Mar-a-Lago first broke, my office immediately reached out to VA requesting information pertaining to the three individuals' influence over the Department. Since then, we have received nothing from VA except excuses."