Poorly considered changes to employment law threaten to derail the manufacturing revival, Welsh companies have warned.
A shake up of default retirement age and paternity leave could wreak havoc on local businesses, WM was told.
Government plans to scrap default retirement age this April has left a "hand grenade on the table", warned Gareth Jenkins, managing director of FSG Tool and Die.
He said: "It's created a situation where you might have a long service employee who feels desperate to work for financial reasons, but he may not be fit enough. You could have a guy who's worked for 40 years who has to be dismissed for capability- which is a bloodbath."
The reforms were fuelling huge uncertainty at businesses, added Louise Terry, training manager at The Royal Mint in Pontyclun.
She said: "With succession planning we try and look at where we need to recruit in what area. Suddenly we have no idea when people are going to retire. What are we supposed to do: guess?"
Manufacturers also warned over potentially "devastating" government plans to extend paternity leave to up to six months.
Reforms must be carefully considered and not rushed through, Jenkins stressed.
"For some businesses like FSG 80% of the engineers are male so a sudden swing from maternity to paternity benefit could wreak havoc... I have nothing against the principle, but let's be careful. The government must think this through, take its time and consult."
Full details of changes to paternity and maternity rights will be confirmed in the budget on Wednesday 23 March.
Chancellor George Osborne is tipped to make firms employing less than 10 staff exempt from new maternity and paternity rules due to come into force this April.