Welsh Secretary Peter Hain has warned MPs will not "rubber stamp" bids to give AMs powers to make Welsh laws.
Mr Hain rejected claims Westminster was blocking some proposals, but said it should be able to "probe their basis".
Addressing the assembly on the Queen's Speech, he also insisted it would be "disastrous" to lose a referendum on law-making powers for Wales.
Mr Hain said he backed the Labour-Plaid coalition but building consensus on powers would "take time".
Plans for a referendum on assembly powers are central to the One Wales deal which formed the basis of the coalition between the two parties after the election.
"There is no cross-party consensus sufficiently wide and deep to win a yes vote now"
Calling for a "mature relationship between Wales and Westminster, Mr Hain said: "Parliament cannot rubber stamp or let anything through 'on the nod'.
"We have no desire to meddle in future policy developments, which are the prerogative of the Welsh Assembly Government and the assembly.
"But it is an important principle that Parliament and Whitehall departments are allowed to probe the basis of legislative requests, and that in doing so are not presented as 'unreasonable' or 'obstructive."
'Sufficient public support'
He said there could be nine new pieces of legislation at Westminster giving the assembly new law-making powers, "nine times the (previous yearly) average".
Mr Hain repeated his warning that calling a premature referendum on transferring full law-making powers to Wales could be "disastrous".
"My overwhelming concern is that we have to win a referendum," he said.
"To lose one would be disastrous.
"There is no cross-party consensus sufficiently wide and deep to win a yes vote now, and nor can we be confident that sufficient public support is there.
"We have to build that consensus, and it will take time," he added.
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