Prospect members will gather with representatives from other Mint unions outside St Stephen's entrance from noon before the lobby that starts at 12.30.

The threat of privatisation was raised in a report published in April which recommended the “introduction of private capital (which) will best allow the business to pursue further commercial opportunities …which come from moving outside the public sector.”

As a result the Mint is to be vested as a government-owned company by the end of the year. But unions at the Mint argue that there is no need to change the existing business model, given its recent record of success, profit generation and meeting all ministerial targets.

They are calling for this success to be consolidated through investment in new technology to develop the business, with any profits returned to the taxpayer rather than a private plc.

On behalf of professional staff at the Mint, Prospect Wales Negotiator Gareth Howells said: “We all know the government is desperate to plug a gap in the public finances resulting from the recession and it seems that that – rather than what would be in the best interests of the Mint and its staff – is behind the drive for vesting.

Howells added that members questioned the wisdom of taking a thriving public service and making it dependant on private capital in the current economic climate.

And he highlight fears over new terms and conditions. “Management have already indicated that staff joining after vesting will be on different arrangements but we do not want a two-tier workforce.”