The Securities and Exchange Commission (SEC) has proposed a ban on flash orders and agreed to tighten the supervision of credit ratings agencies.
Flash trades, where users are given an advanced peek at unfilled orders ahead of the wider market, have been under the spotlight recently, with two US senators calling for their ban.
Nasdaq OMX and Bats Exchange both dropped the practice voluntarily last month while Nyse Euronext has never offered flash trades.
However, last month, the boss of Direct Edge, which pioneered the introduction of flash order types three years ago, launched a robust defence of the controversial practice.
The SEC has now unanimously proposed to ban the practice which would effectively prohibit all markets - including equity exchanges, options exchanges, and alternative trading systems - from displaying marketable flash orders.
Mary Schapiro, chairman, SEC, says: "Flash orders may create a two-tiered market by allowing only selected participants to access information about the best available prices for listed securities."
The SEC is expected to follow up the flash order proposal by tackling other market areas, including the use of dark pools.
Separately, the watchdog has voted to bolster oversight of credit ratings agencies. The move is designed to reduce conflicts of interest at the firms, which have been criticised for contributing to the subprime mortgage crisis and subsequent financial meltdown.