The Bill, Hillary and Chelsea Clinton Foundation announced late Monday that it had amended its tax returns for the last four years to more accurately account for revenue received from government sources.

In a statement, Clinton Foundation President Donna E. Shalala said the revised returns came as the result of a voluntary review of the global charity’s past tax returns. She said the changes were not required by law and did not indicate that the charity owed any money to the Internal Revenue Service.

Still, the amendments, which came in response to increased scrutiny on the charity as a result of Hillary Rodham Clinton’s presidential campaign, are sure to raise new questions from conservative critics of the foundation.

Founded by former president Bill Clinton initially to raise money for a presidential library, the foundation has become a $2 billion charitable behemoth, devoted to combating global poverty, improving health care and promoting education around the world.

The amendments came as the foundation filed its tax return for the 2014 calendar year, indicating it raised $177.8 million in the year preceding Hillary Clinton’s presidential run.

Shalala said the amendments were a result of the foundation’s commitment to “disclosure and thoroughness” and came as a result of a review of the charity’s past returns conducted by Kathy Keneally, a former assistant attorney general who now works for the firm DLA Piper. The Foundation had indicated it was likely to amend its returns in April to better reflect government funding.

According to Shalala, past returns accurately reflected the Foundation’s overall revenues and spending. Still, she said the forms had failed to properly account for the sources of the charity’s revenue, particular failing to note millions in government grants.

Shalala said “there is no change in our bottom line numbers: assets, liabilities, and net assets.” She said the decision to refile was based on the fact that the tax return “serves as a public disclosure document for our friends, supporters, partners, and the general public.”

The Foundation indicated that the amended forms also better denoted millions in income to the foundation that came as a result of speeches given to benefit the organization by Bill Clinton, as well as Chelsea Clinton.