A new rule forcing U.S. companies to disclose the ratio between their chief executive's pay and that of the typical employee is a "logistical nightmare"", lawyers say.

"It's just not do-able for a large company with tens of thousands of employees worldwide," Richard Susko, a partner at Cleary Gottlieb told The Financial Times.

The median pay package for S&P 500 CEOs was $7.5 million in 2009, according to pay research firm Equilar. The average pay in the private sector was just over $40,000.

Businesses are preparing to lobby the SEC, which has to write detailed provisions for the new rule.

The office of Senator Robert Mendez (D., N.J.), who proposed the rule, dismissed the criticism.

"The idea behind the new rule is that sunlight is the best disinfectant," an aide told the FT. "Disclosure will help encourage fair pay for workers at a time when middle class pay has stagnated while CEO pay has skyrocketed."