It is no longer good enough for limits on the power of the House of Lords to rely on decades-old conventions, says a group of Labour peers.
There are 92 remaining hereditary peers in the Lords
A Labour working group on the powers of the Lords says the party must include reform plans in its next manifesto.
It wants a new system for tackling differences between MPs and peers and other measures to ensure the primacy of the House of Commons.
The government has dropped plans for Lords reform before the next election.
That decision angered some peers who wanted the 92 remaining hereditary peers removed from the House of Lords.
The working group only examined the powers of the Lords, not its composition, but its plans have still provoked concern among opposition peers.
Under the Salisbury Convention, the Lords should not wreck or vote against government manifesto commitments at second and third reading.
But such conventions are not set out in law, nor are they even in Parliament's internal rules, so they can be ignored, says the report.
The peers say with opposition peers being more assertive there is confusion about the Lords' powers and "considerable uncertainty about its relationship with the elected House of Commons".
Lord Hunt of Kings Heath, who chaired the working group, said: "It is vital that the House's powers are defined with clarity and precision.
"Relying on informal understandings and conventions which can be broken at any time is no longer sustainable."
The group recommends:
- Making Bills which enter Parliament through the Lords subject to the Parliament Act. This would let the government force through such Bills - something it is not able to do now peers have rejected key parts of its legal reform plans
- Introducing reconciliation systems between the Commons and Lords to help resolve differences
- Creating a reasonable time limit for all Bills to complete their Lords' stages
- Allowing peers to use their delaying powers on secondary legislation
- Better support to help backbench peers scrutinise legislation and paying opposition party frontbenchers.
The government has failed to reach consensus on the membership of the Lords, including whether some or all peers should be directly elected.
The report, which has been endorsed by the Labour group in the Lords, stresses the inquiry did not examine the composition problem.
But it says establishing a clear view on Lords' powers would help decision making on the membership question.
It urges action on reform "as quickly as possible" and says Labour should commit to reforming the Lords' conventions, powers and procedures in its next election manifesto.
Lord Chancellor Lord Falconer, welcomed the report and said the peers had brought expertise to the reform debate.
"Labour is committed to bringing forward proposals on the future of the House of Lords in its election manifesto," he said.
"This report will be important in helping shape the party's and the government's thinking on the way ahead."
Conservative Lords leader Lord Strathclyde said the report contained some thoughtful proposals which the Tories might support.
"But alongside those are less welcome ideas - whose overall effect would be to strengthen government and weaken Parliamentary opposition," he said.
Lord Strathclyde also insisted the Tories had not broken any parliamentary conventions.
Liberal Democrat constitutional affairs spokesman Lord Goodhart raised similar concerns.
"This report contains a number of interesting proposals, but it does not go deeply enough into the implications of them, some of which would seriously damage the effectiveness of the Lords," he said.