Peter Hain was last night accused of meddling in the Assembly's affairs after announcing plans to ban regional AMs from calling themselves 'local'.
He said next year's Government of Wales Bill would be changed to force the Assembly to draw up a new Code of Conduct - similar to that used in the Scottish Parliament - to prevent the 20 regional members claiming to represent individual constituencies.
But Presiding Officer Lord Elis-Thomas accused him of 'interference', and opposition leaders lined up to warn him to keep out of internal Assembly matters.
Although Mr Hain can insist on the creation of a new Code of Conduct, AMs will decide the precise wording themselves.
The Welsh Secretary also wants to see a crackdown on the expenses paid to regional AMs - at the moment all AMs get the same amount - but concedes he can only 'strongly encourage' the Assembly to take action .
The changes follow a bitter row between Labour and the opposition over the role of regional AMs, who are elected on a top-up PR list.
Many Labour AMs are infuriated by what they see as attempts by regional AMs - all of whom come from opposition parties - to muscle in on their territory and use their position to campaign in individual constituencies.
The row culminated in the leaking of a memo written by Plaid AM Leanne Wood, which suggested taking on constituency case work was a 'waste of time' for regional AMs.
Mr Hain said, 'I'm announcing today that the Wales Bill will ensure that Assembly Members cannot misrepresent their mandate. No more list members dishonestly posing as constituency AMs.
'It is also high time list members stopped abusing taxpayers' money running rival constituency offices to the local members they were defeated by, effectively tax-funded campaign offices. It is an abuse of democracy and the Assembly should act to stamp it out.'
The plans have been agreed with Rhodri Morgan, a spokeswoman for the First Minister confirmed.
Last week Mr Hain called on pro-devolution parties like Plaid Cymru and the Liberal Democrats to 'grow up' and back his Bill. But the latest proposal is unlikely to increase cross-party support.
Lord Elis-Thomas said, 'We will continue to treat AMs equally unless a change in legislation compels us to do otherwise.
' I do not see the need for a change, and I regard this as interference from the Secretary of State, which is not what devolution is supposed to be about.'
Plaid Cymru's Assembly leader Ieuan Wyn Jones said the plans would 'undermine the basis of democracy in Wales and create a two-tier system'. He added, 'It cannot be a coincidence that this issue was never raised in the four years when New Labour had regional AMs themselves.'
Mike German, leader of the Liberal Democrats in the Assembly, said
the current system gave voters a choice of which AM they contacted.
'This change is anti-democratic and must be resisted,' he added.