Preseli Pembrokeshire AM Paul Davies says the county's bus services are simply not good enough.
He told the Labour-led Assembly Government that the public transport network in Pembrokeshire is failing the most needy in society.
"It is a worrying issue for many of my constituents, who already feel isolated by the rurality of the county," he told the Senedd.
"It is nearly always the most vulnerable members of our communities who suffer in situations such as this."
"Bus services are essential to people who do not have access to
other means of public transport, such as rail links, or do not have the means to fund private transport.
"A lack of mobility also tends to limit individuals' opportunities for employment, consumption and social activity."
Two weeks ago he told the First Minister that bus routes in Pembrokeshire could be affected because of delays in getting Government grants that help pay for them.
And last week he highlighted problems with the infrequency of buses in the county.
"I have been contacted by numerous constituents who are worried about bus services in the wake of recent post office closure announcements," he said.
"Many people will now find themselves unable to walk to their local post office and will have no option but to travel to other post offices.
"There is a growing concern in many parts of Pembrokeshire that current bus services do not encompass the revised post office locations and opening hours."