Labour will push for a vote on Boris Johnson's decision to water down a code on breaches of ethics rules - including his own.
The Prime Minister on Friday issued a new version of the ministerial code - allowing ministers to commit minor breaches without resigning.
The vow that ministers must "uphold the very highest standards of propriety" was removed from the revamped edition.
And a foreword no longer explicitly mentions the seven Nolan principles of public life - integrity, objectivity, accountability, transparency, honesty and leadership in the public interest.
Meanwhile Mr Johnson dismissed calls from his ethics advisor Lord Geidt, to be able launch investigations into behaviour without the PM’s permission.
Under the peer's revised terms of reference, there will be an "enhanced process" to enable him to initiate inquiries, but he will still require the Prime Minister's consent before going ahead.
Deputy Labour leader Angela Rayner accused the Prime Minister of acting like a " tinpot despot" with the revisions announced last week.
Leader Keir Starmer and his team plan to force a vote in an opposition day debate when Parliament returns from its week-long break to mark the Queen's Platinum Jubilee.
With its next opposition day debate, Labour is set to ask MPs to enshrine the commitment that ministers who commit serious breaches of the ministerial code will have to resign.
Labour aims to put Tories in an awkward situation after a similar vote on the Government's attempt to rip up Commons standards rules - in a bid to prevent former cabinet minister Owen Paterson from being suspended for lobbying - ended with accusations of sleaze levelled at Mr Johnson's administration.
Ms Rayner said: " Boris Johnson is behaving like a tinpot despot and is trampling all over the principles of public life.
"Many decent Conservative MPs are deeply uncomfortable with Johnson's behaviour and they now have the chance to stop his sinister attempts at watering down standards and integrity in our democracy.
"Serious breaches of the ministerial code must result in resignation, whether they are deliberately misleading Parliament, bullying staff, bribery or sexual assault.
"This Prime Minister simply cannot be trusted to uphold standards in Government while his conduct sinks further into the gutter and he gives the green light to corruption."
A Government policy statement said it was "disproportionate" to expect ministers to resign or face the sack for "minor" violations of the code.
The update gives the Prime Minister the option of ordering a lesser sanction such as "some form of public apology, remedial action or removal of ministerial salary for a period".
The changes come days after the final report by senior civil servant Sue Gray into lockdown parties at Downing Street led to renewed calls for Mr Johnson to resign.
The Tory leader faces an inquiry by the Commons Privileges Committee into whether he misled Parliament with his regular reassurances that Covid rules were upheld at No 10 during England's lockdowns.
It comes after the Home Secretary was allowed to stay in post despite being found to have bullied Home Office staff.
Mr Johnson stood by Priti Patel in a move that saw Lord Geidt's predecessor, Sir Alex Allen, resign in November 2020.
