WASHINGTON  Under pressure from liberal critics, Justice Clarence Thomas of the Supreme Court acknowledged in filings released on Monday that he erred by not disclosing his wife’s past employment as required by federal law.

Justice Thomas said that in his annual financial disclosure statements over the last six years, the employment of his wife, Virginia Thomas, was “inadvertently omitted due to a misunderstanding of the filing instructions.”

To rectify that situation, Justice Thomas filed seven pages of amended disclosures listing Mrs. Thomas’s employment in that time with the Heritage Foundation, a conservative policy group, and Hillsdale College in Michigan, for which she ran a constitutional law center in Washington.

The justice came under criticism last week from Common Cause, a liberal advocacy group, for failing to disclose Mrs. Thomas’s employment as required under the 1978 Ethics in Government Act. While justices are not required to say how much a spouse earns, Common Cause said its review of Internal Revenue Service filings showed that the Heritage Foundation paid Mrs. Thomas $686,589 from 2003 to 2007.