Staff at an Anglesey hotel have been banned by managers from speaking Welsh when the head chef is in the kitchen.
The Carreg Mon near Llanfairpwll asked employees not to use Welsh because he does not speak the language and is responsible for health and safety.
The Welsh Language Board (WLB) is to write to the hotel and wants a meeting with the managers.
General manager Ruth Hogan insisted the hotel was not discriminating against the language.
Of its 25 staff, only three are non-Welsh speaking.
She said that there was "no issue about the Welsh language here".
"If anything we encourage the Welsh language to be spoken here. There is absolutely no discrimination against the Welsh or English language here, it's only about safety standards."
A WLB spokesperson said: "With more than 60% of the island's population speaking the language, a figure which rises to 87% in some communities, Anglesey is one of the strongholds of the Welsh language
"It is therefore a shock and a great disappointment that an employer on the island takes this stance against the language."
The WLB added: "This could be a matter the Equalities and Human Rights Commission may want to take up. Under current legislation, the Welsh Language Board's powers do not cover such instances.
"But it is a clear example why protecting people's freedom to speak Welsh at the workplace has been included in the new Welsh language legislation, which will come to force next year."