The Arts Council has frozen €300,000 in funding for The Abbey Theatre.
It follows concerns the national theatre has been buying in more productions from abroad.
Irish theatre makers say that has resulted in a big drop in opportunities for them.
A letter detailing a range of issues has been signed by hundreds of people, including big-name actors.
Aidan Gillen, Ruth Negga and Tom Vaughan-Lawlor are among those to add their signatures.
The Arts Council has told The Abbey Theatre its funding will be restored once it improves employment opportunities for Irish-based artists.
The theatre says it's taking the concerns "very seriously".