Don Foster, the party's education spokesman, has discovered that Labour changed the rules when it came to power in May 1997, to allow the written briefing of Labour MPs.
Mr Foster has asked Lord Neill of Bladen, who heads the Committee on Standards in Public Life, to look at the issue. The committee is currently considering the role of special advisers, whose numbers have swelled under Labour.
"When special advisers were first introduced, their role was to provide a party political balance for ministers, not brief-ings for backbench MPs," Mr Foster said. "This now amounts to an unfair advantage for the party in government and a gross misuse of taxpayers' money."
A model letter of appointment for special advisers under the Conservatives said: "You should not engage in activities likely to give rise to criticism that you are being employed at public expense for purely party political purposes."
Andrew Tyrie, a Conservative MP and former special adviser, has told the committee that when Margaret Thatcher came to power in 1979 she appointed seven advisers. By early this year, the number had risen to more than 70, with 20 in Downing Street alone.
A Cabinet Office spokesman said special advisers' terms and conditions had been similar under the Conservatives.Reuse content