Gotham Writers' Workshop was created in 1993.
Writers Workshop was created in 1958.
Asian American Writers' Workshop was created in 1991.
Erma Bombeck Writers' Workshop was created in 2000.
That would depend totally on its meaning. If the workshop belongs to the writers or writer then you would use the apostrophe for the possessive. However, if you are saying it is a workshop for writers then the plural is correct.
Gotham Records was created in 1946.
Gotham Gazette was created in 1999.
Gotham - typeface - was created in 2000.
Gotham Stakes was created in 1953.
Gotham Hall was created in 2002.
The web address of the Asian American Writers Workshop is: http://aaww.org
Lunch at the Gotham Café was created in 1997.
Gotham Girls was created on 2000-07-27.