The American Beauty star serves as artistic director of the Old Vic Theatre in London, but he's worried young people are being priced out of the West End.
Executives at the Old Vic have recently announced a subsidised ticket scheme for under-25s - and Spacey wants more theatres, both in the U.K. and America, to offer similar initiatives.
He tells London's Evening Standard, ""When I look around at Broadway and the West End, theatre is becoming an exclusive club.
""(It's unaffordable) if you don't have £115 to spend, and that's not talking about parking, dinner, the baby-sitting and everything else. Kids are not going to spend that kind of money. They're going to buy iPads, save the money, or do something else.
""As the generation that is going passes on, the question is who is going to replace them? If we don't reach out to make theatre affordable to the young generation we will lose them all. It is so short-sighted not to think about your future audiences.
""In this climate we need more than ever for companies to step up and support initiatives that make theatre accessible, especially to young people. Exposure to the arts and culture is enormously valuable.""