Paula Barker has pressed ministers to review gaps in Royal Mail regulation after warning that delayed hospital, court and social-security letters were harming vulnerable people.
The Liverpool Wavertree MP said first-class delivery targets had been missed since 2017 while stamp prices had risen and regulatory standards had been relaxed.
She highlighted bulk mail that sits outside the universal service quality targets, even though it includes correspondence on which people depend.
Future of Work Minister Kate Dearden said Royal Mail's performance had been unacceptable for too long and specifically acknowledged operational problems at the Lark Lane and Liverpool North delivery offices.
Dearden said Ofcom should consider the role of bulk mail and whether additional regulatory measures were needed to secure reliable service for all postal customers.
No regulatory change has yet been agreed. The intervention places excluded correspondence within Ofcom's continuing consideration of service standards.
