WASHINGTON (Reuters) - Four Democrats on the Senate Banking Committee have called for an investigation into whether the acting chairman of the U.S. Securities and Exchange Commission exceeded his authority by taking steps to scale back or delay rules required by the 2010 Dodd-Frank law.

In a letter to the SEC’s internal watchdog, Inspector General Carl Hoecker, the Democrats said acting SEC Chairman Mike Piwowar should not have ordered staff to review the SEC’s rules on “conflict minerals” and CEO pay ratios because they are mandated by Congress.

Both rules are part of Dodd-Frank, which was passed in 2010 to prevent a repeat of the financial crisis. Republicans have been highly critical of the law, saying its regulatory requirements are too burdensome for businesses.

“We ask that you conduct an investigation into each of these decisions to determine whether they are legally permissible, and in keeping with the SEC’s core mission,” wrote the lawmakers, which include Elizabeth Warren of Massachusetts, Sherrod Brown of Ohio, Robert Menendez of New Jersey and Brian Schatz of Hawaii. Brown is the top Democrat on the committee, which has 12 Republicans and 11 Democrats.

Christopher Carofine, a spokesman for Piwowar’s office, declined to comment. A spokesman for the inspector general’s office could not be immediately reached for comment.

In Wednesday’s letter, the lawmakers also complained because Piwowar recently revoked the power of certain mid-level managers in the enforcement division to issue subpoenas, and vested the power solely with the unit’s director.

Decisions on how to delegate such authority rest with the SEC chair and do not require a commission vote.

Similarly, while the SEC chair cannot adopt rules unilaterally, SEC rules give the chairman fairly broad latitude to take other actions, such as hiring or directing staff to review rules.

Piwowar, a Republican, became the temporary head of the SEC in January. President Donald Trump’s choice for SEC chairman, Jay Clayton, is awaiting Senate confirmation.

Piwowar announced in late January he had asked staff to review prior compliance guidance on the conflict minerals rule to determine if “additional relief” is appropriate. He took similar steps with the CEO pay rule a few days later.

The conflict minerals rule requires companies to tell investors if their products contain certain minerals from a war torn part of Africa.

The CEO pay ratio rule requires companies to provide a ratio comparing their chief executive officer’s pay to the median workforce, and is set to start appearing in corporate filings during the 2018 proxy season.