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.