WASHINGTON (Reuters) - The U.S. Congress’ watchdog office has agreed to investigate President Donald Trump’s commission on voter fraud after three Democratic senators raised concerns the panel’s work may diminish the public’s confidence in the democratic process. The Government Accountability Office said in a letter dated  on Wednesday that it had accepted a request from Democratic  Senators Amy Klobuchar, Michael Bennet and Cory Booker to investigate the Presidential Advisory Commission on Election Integrity. Trump established the panel in May after charging, without evidence, that millions of illegal immigrants voted in the November 2016 election. Most state election officials and election law experts say that U.S. voter fraud is rare. Democrats and voting rights groups have criticized the panel, arguing it could be a vehicle for changes that would make it harder for lawful voters to cast ballots. A number of state governments have declined to hand over information about their voters to the White House. In a letter last week to the GAO requesting the probe, the three senators said the commission, which is headed by Vice President Mike Pence, had not responded to congressional requests for information about its activities. They said the panel’s lack of transparency could “unnecessarily diminish confidence in our democratic process.” The White House did not immediately respond to a request for comment on the GAO’s decision to open an investigation.  The commission’s vice chair, Kris Kobach, the Republican secretary of state for Kansas and an advocate of tougher laws on immigration and voter identification, asked states in June to turn over voter information. The data requested by Kobach included names, the last four digits of Social Security numbers, addresses, birth dates, political affiliation, felony convictions and voting histories. More than 20 states refused outright and others said they needed to study whether they could provide the data. 