Reeves warned that Burnham "risks going the way of Liz Truss" after he suggested Britain should not be "in hock to the bond markets" regarding borrowing.
The comparison underscores escalating tensions between Sir Keir Starmer's supporters and Burnham, amidst speculation of his potential leadership ambitions.
Reeves stressed the importance of fiscal responsibility, stating she would make difficult decisions to reduce national debt and borrowing costs as Chancellor.
Sir Keir also drew a similar comparison, linking Burnham's stance on fiscal rules to the "disaster" of the Liz Truss government's economic policies.