A fourth member of the National Rifle Association's Board of Directors has resigned. The string of vacancies on the top gun advocate's board comes amid a rash of inner turmoil and renewed scrutiny in the wake of two deadly mass shootings earlier this month.

Julie Golob, a professional sport shooter, wrote a resignation letter on her personal blog posted on Tuesday, saying she can "no longer commit to fulfilling the duties of a director."

"My intentions in running as well as serving in this volunteer position are directly aligned with the purposes and objectives of the organization. I am proud to have had the opportunity to represent the members of the National Rifle Association," she added. Golob leaves her tenure on the board without completing the standard full 3-year term.

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"I wish the director who fills my vacancy and the rest of the board nothing but success. I will absolutely continue to support the NRA's programs and sports as a proud benefactor member and active participant in the preservation of freedom," Golob wrote.

Golob's exit comes on the heels of three other members' departure from the board, all of whom cited concerns over questionable spending by the group's leaders. The members claimed they were "stripped of committee assignments" after they "sought information" about the "allegations of impropriety."

In recent days, leaked documents showed the group's longtime leader Wayne LaPierre may have misused member dues, spending nearly $300,000 on designer clothes over 10 years and charging the NRA for luxury travel to the Bahamas, Budapest and Italy. Rising costs and controversy also led the group to shutter its entertainment arm -- NRATV.

Earlier this year, the organization's president Oliver North was pushed out of leadership after raising concerns about the NRA's finances. LaPierre accused North and NRA's top lobbyist Chris Cox of extortion at the time.

Now the group's tax-exempt status is being investigated by both the New York and D.C. attorney general. Despite the growing exodus of leadership roles, the NRA still has deep pockets. It took in $170 million in member dues alone last year and, according to FEC filings from the presidential election, it has the president's ear after spending $30 million to help him get elected in 2016.