Democratic U.S. Senator Elizabeth Warren issued a scathing critique of Securities and Exchange Commission Chair Mary Jo White, citing executive pay rule delays and inadequate enforcement in the lawmaker's latest swing against the Obama administration's financial policies.

In a 13-page letter on Tuesday, Warren laid out numerous concerns over how White has run the agency.

"You have now been SEC Chair for over two years, and to date, your leadership of the commission has been extremely disappointing," wrote the Massachusetts senator.

Although U.S. lawmakers often criticize policymakers, the blunt letter from Warren is unusual because White, an independent, was nominated by Democratic President Barack Obama.

Warren, however, has not been shy about condemning members of her own party. Most recently, she criticized Obama for seeking "fast-track" negotiating authority on a Pacific Rim trade deal.

In response, White said she was proud of her work, saying the SEC has advanced more than 30 congressionally mandated rulemakings and other initiatives to protect investors.

"Senator Warren's mischaracterization of my statements and the agency's accomplishments is unfortunate, but it will not detract from the work we have done, and will continue to do, on behalf of investors," White, who took over the SEC in April 2013, said in a statement.

While White has won praise from many, she has also faced criticism from liberals like Warren who want stronger checks on Wall Street.

Warren's views on enforcement policy often align with SEC Commissioner Kara Stein, another Democrat who frequently clashes with White.

Last year, Stein began rejecting some of the SEC's decisions to grant regulatory waivers to big banks that break the law. Such waivers allow banks to continue their usual securities business despite criminal convictions or civil fraud charges.

Warren in her letter raised concerns about the waivers, saying recent ones for banks that rigged foreign exchange rates reflect the SEC's view that they "deserved to continue to enjoy special privileges."

She also accused White of misleading her during a May 21 meeting in which Warren asked why the SEC has still not adopted rules requiring companies to disclose the ratio of pay between the median worker and the chief executive.

According Warren, White pledged the rules would "be done by fall." Later that day, however, the SEC said in a calendar listing they would be completed in April 2016.

On Tuesday, Warren demanded an explanation from White about her statements on the rule's timing. An SEC official, speaking on background, said such calendars represent the end of the year's working period, not an exact deadline, adding that White still plans to complete the rule by autumn.

Warren also asked for a list of all waiver decisions since January, among other demands.

Warren had been pushed to run for the 2016 Democratic presidential nomination as a more progressive voice, although she said she is not seeking the nomination. On Tuesday, the political group MoveOn.org suspended its "Run Warren Run" campaign.