The current cap is just over £2.2million, but a series of allowances covering aspects such as large squad sizes and long-term injuries, can take the threshold up to £3.4million.
The salary cap was introduced nine years ago in an attempt to ensure that the Premiership remained an evenly contested tournament.
The board of Premier Rugby, the umbrella organisation that represents the 12 Premiership clubs, will vote later this month on a proposal to abolish the allowances and set an inclusive figure of £4 million.
