Many firms remain hesitant to speak on the record. But one of the conditions for membership in the new industry group, called the Principal Traders Group, is that firms identify themselves publicly on its Web site.

The group comprises 31 firms. According to data calculated in June, its biggest members spent $690,000 on lobbying last year, more than double what they spent in 2009. They gave more than $547,000 to lawmakers’ political campaigns in 2010, on top of the $456,000 they handed out in the last political cycle in 2008.

High-frequency techniques are used by Wall Street banks and hedge funds, but it is the new independent firms that account for the bulk of this new kind of activity. Most of them were founded in the last 10 to 12 years. Many are still relatively small, employing a dozen to a hundred people, though some have as many as 250.

Trading mostly with their owners’ money, they scoop up hundreds or thousands of shares in one transaction, only to offload them less than a second later before buying more. They can move millions of shares around in minutes, earning a tenth of a penny off each share.

As a group, they earned $12.9 billion in profit in the last two years, according to the Tabb Group, a specialist on the markets. Tabb expects their earnings to slow this year as Wall Street’s big brokerage firms fight back with their own faster computerized trading.

The S.E.C. started to think these firms needed tighter controls in early 2009 when analysts for the first time began to point to the sector’s billions in profit, and critics wondered whether their technological firepower gave them an unfair advantage.