Enforce rules; SAYS.
The Cabinet Minister's job as Gordon Brown's "enforcer" puts him at the top of the Westminster tree.
If you've been a naughty Labour MP, then get ready to slink to Mr Byrne's office with your tail between your legs.
But as sleaze watchdogs prepare to carry out their second investigation in as many years into his activities, it's Mr Byrne himself who faces a grilling.
He stands accused of misusing envelopes that were pre-paid and House of Commons-franked.
It's not exactly Jacqui Smith's husband's porn collection, but it raises questions about his judgement.
If the man enforcing the cabinet rules can't be trusted, then who can?