The Prime Minister has been warned against the use of so-called Henry VIII clauses which would allow her to avoid full parliamentary scrutiny of the Brexit process.
At the Conservative Party Conference last autumn, Theresa May announced her government would introduce a Great Repeal Bill to end the supremacy of EU law in the UK, a crucial part of leaving the European Union.
Senior peers on the House of Lords Constitution Committee said Theresa May must not use the legislation to "pick and choose" which elements of European law she wanted to scrap or alter without Parliament's full involvement.
The committee said a distinction must be drawn between the move to transfer EU regulations into UK laws and any subsequent attempt to change them after Brexit.
The committee noted that the Great Repeal Bill was "likely to involve a massive transfer of legislative competence from Parliament to Government", and stressed that a balance between the two must be struck.
The committee's chairman, Lord Lang, said it was important to get the safeguards right, particularly given the Brexit campaign promise to "take back control".
The peers also called for an enhanced scrutiny process for secondary legislation laid under the Great Repeal Bill to ensure that Parliament was not sidelined by ministers.
Where ministers want to change the law - such as by introducing a new immigration regime - they should be required to go through the full procedure required for an Act of Parliament, the peers said.
Ministers should only be allowed to make changes to existing legislation without the full scrutiny process, when making minor adaptations to EU law so that it would fit in the UK's framework and to allow for a swift response to Brexit negotiations.
Lord Lang, a Tory former Cabinet minister, said the Bill would be "an extremely complicated piece of legislation" and the Government might need to be given "wide-ranging powers" over the process of turning EU legislation into domestic law.
"Those powers should not, however, be used to pick and choose which elements of EU law to keep or replace - that should be done only through primary legislation that is subject to proper Parliamentary scrutiny," he said.
"Scrutiny must not be sidelined. There must be: a clear limit on what the delegated powers in the Bill can be used to achieve; a requirement for ministers to provide Parliament with certain information when using those powers; and enhanced parliamentary scrutiny of the exercise of those powers."
Conservative former attorney general Dominic Grieve, a leading supporter of Open Britain, said: "Any changes to the law must involve a full Act of Parliament, not a secondary legislative device which bypasses Parliamentary scrutiny."
Liberal Democrat leader Tim Farron said Ms May was "playing with fire" over the Repeal Bill.
"The Government cannot use the Great Repeal Bill to get their own way," said Mr Farron.
"If the Government has found the Article 50 Bill difficult, they should be under no illusion - this will be hell.
"For all Theresa May's talk of giving power to the people she is increasingly fighting to ensure that the whole Brexit process occurs behind closed doors with only her inner circle having any say.
"These vital protections, from workers' rights to the environment, matter, and we will defend them to the hilt."