Two top Democrats on the House Judiciary Committee called for a hearing Tuesday to examine a Montana judge's conduct in forwarding an email that included a racist joke involving bestiality and President Barack Obama's mother.

Reps. John Conyers of Michigan and Steve Cohen of Tennessee told Committee Chairman Lamar Smith, R-Texas, in their letter that the committee has a duty to investigate the potential consequences of Judge Richard Cebull's email.

"At a minimum, forwarding this email illustrates poor judgment and of conduct that was unbecoming of a federal judge," they wrote. "More troubling, however, is the possibility that public disclosure of the judge's conduct may not only undermine the public's view of his personal credibility and impartiality as a judge, but also the integrity of the ... federal judiciary."

A hearing would determine whether further investigation or legislative action was needed, they wrote. Congress can remove a federal judge for misconduct by impeachment in the U.S. House of Representatives and Senate confirmation, but such action is rare.

Smith had no immediate response to their hearing request.

At least three complaints have been filed with the San Francisco-based 9th U.S. Circuit Court of Appeals against Cebull regarding the email, which he forwarded to six friends on Feb. 20. One of the complaints was filed by Cebull himself. He asked 9th Circuit Chief Judge Alex Kozinski "to conduct an inquiry as to whether recent activity of mine constitutes misconduct."

Cebull did not return a message from The Associated Press on Tuesday. He has previously said that he forwarded the email because he disliked Obama and denied allegations of racism. News of the email broke Thursday when it was forwarded to a Great Falls Tribune reporter.

The judge sent Obama a letter of apology Thursday in which he said he accepted responsibility, assured the president that it will never happen again and said he had asked for a judicial review.

"Honestly, I don't know what else I can do," Cebull wrote. "Please forgive me and, again, my most sincere apology."

The White House confirmed Tuesday that it had received the letter.

Cebull was nominated by former President George W. Bush and received his commission in 2001. He has served as chief judge of the District of Montana since 2008.

The two other known complaints have been filed by the good-government advocate, Common Cause, and by the Montana Human Rights Network.

David Madden, the assistant executive for the 9th Circuit, declined to say whether other complaints have been filed, citing confidentiality in the judicial misconduct process. Cebull and the other groups waived confidentiality when they filed their complaints, he said.

"We have acknowledged receiving Judge Cebull's complaint and announced that the matter will be investigated. That is the extent of what we can say publicly at this time," Madden said.

The 9th Circuit has the ability to censure or reprimand the judge, order that no new cases be assigned to him for a designated period of time or ask the judge to retire. If the conduct potentially constitutes grounds for impeachment, the 9th circuit could refer the matter to the Judicial Conference of the United States, which oversees the federal court system.

Conyers and Cohen wrote that a legislative inquiry is necessary regardless of the results of the 9th Circuit's conclusions.

The last federal judge to be impeached and convicted was U.S. District Judge G. Thomas Porteous of Louisiana in 2010. Prosecutors said gambling and drinking problems led Porteous to begin accepting cash and other favors from attorneys and bail bondsmen with business before his court.