Washington (AFP) - A powerful US senator demanded Friday that President Barack Obama remove the head of the Securities and Exchange Commission for allegedly obstructing efforts to force companies to reveal political donations.

Democratic Senator Elizabeth Warren escalated her longstanding criticism of SEC Chair Mary Jo White, sending a letter to Obama calling White the "biggest barrier" to establishing rules that require companies to disclose political contributions.

"For years, the chair of the SEC, Mary Jo White, has refused to develop a political spending disclosure rule despite her clear authority to do so, and despite unprecedented and overwhelming investor and public support for such a rule," Warren said. "Enough is enough."

Warren said Obama should invoke his unilateral authority to immediately name a new SEC chair from the agency's five-member commission.

"While demoting an existing chair and selecting another from among the agency's current Commissioners would be an uncommon act, Chair White's extraordinary, ongoing efforts to undermine the agency's central mission make such a step necessary," she said.

The SEC creates and enforces the rules governing public companies and the securities industry. Its commission is effectively chosen by the two political parties, but the chair is named from the commission by the president.

The issue of political disclosures has mounted as businesses and foundations have deployed hundreds of millions of dollars, often secretly, to back candidates from both parties in this year's elections.

Warren said that although the Obama administration and his Democratic Party have supported forcing such disclosures, Republicans in Congress have fought legislation and White has resisted putting the requirement in SEC rules for the thousands of public companies it regulates.

Serving on the powerful Senate banking committee, Warren has made herself a force in corporate and financial services regulatory issues.

While her voice alone might not bring the Obama administration, in its final three months, to take action on White, Warren is thought to be powerful enough to make some demands on Hillary Clinton if the Democratic candidate wins the November White House race.