More than a dozen federal appeals court judges have violated federal conflict-of-interest laws over the past three years, throwing into doubt decisions in 26 cases, according to an analysis from a watchdog group.

The Center for Public Integrity, in a report being released Monday, found 24 cases in which judges ruled despite owning stock in a company appearing before them. In two other cases, the judges had financial ties to law firms representing one of the parties.

When informed of the conflicts, all 16 judges sent letters to the parties involved in the cases, disclosing the violations. Several judges said their failure to withdraw from the cases was an oversight, the report said. Some of the judges had conflicts in more than one case.

In one 2011 case, Judge James Hill of the 11th U.S. Circuit Court of Appeals in Atlanta was part of a three-judge panel that affirmed a lower court verdict in favor of health care giant Johnson & Johnson in a lawsuit over a malfunctioning medication pump. At the time of the decision, Hill owned as much as $100,000 in Johnson & Johnson stock, the report found.

The conflicts took place despite a new policy adopted by the Judicial Conference of the United States in 2006 that requires all federal courts to conduct automated screenings to help avoid potential conflicts of interest. Judges must disclose a list of their financial holdings and each court is required to screen for conflicts on a regular basis. But the database is only as good as the information provided by judges.

More than half of all appellate judges own corporate stock, according to the report.

Federal law requires judges who own even one share of stock in a company appearing before them to disqualify themselves from the case. The investigation reviewed the three most recent years of financial disclosure reports from 255 of the 258 judges who sit on the country's 13 federal appeals courts, and compared them against cases to determine conflicts.

In each case, the judge with the financial conflict was part of a three-judge panel deciding the case.

There is no penalty for judges who fail to withdraw from cases involving a conflict of interest. The judge must simply notify the parties involved and give them an opportunity to object. The appeals court can then decide whether to rehear the case with a different panel of judges.

David Sellers, a spokesman for the Administrative Office of the U.S. Courts, told the center that federal judges take their ethical responsibilities seriously. He attributed the mistakes to human error and noted that the cases flagged in the report represent just a fraction of the 109,000 total cases decided by federal appeals courts over the past three years.