Preseli Pembrokeshire AM Paul Davies says not enough is being done to safeguard tax office jobs in Haverfordwest.
He is appalled that Wales' deputy first minister, who has responsibility for the economy, has not been in touch with Westminster over the issue.
"Protecting high quality jobs should be a priority for any Government, particularly in the current vulnerable economic circumstances," he told Ieuan Wyn Jones at the Senedd.
"These jobs contribute enormously to the local economy and the tax office offers an essential service to businesses and individuals in the area."
Mr Wyn Jones said that while the First Minister had been in touch with the Government, he personally had not had direct dealings.
"I am horrified to hear that he has not been in touch about this issue – Welsh jobs are his responsibility," added Mr Davies.
"I have now written to him urging him to lobby Westminster on behalf of the workers in Haverfordwest."