In the United States, perpetual copyright is prohibited by its Constitution, which provides that copyright is "for limited times". However, it neither specifies how long that term can be, nor does it impose any restriction on the number of times the term may be extended. Indeed, since the enactment of the Copyright Act of 1790, copyright term has been successively extended by Congress on four occasions, retroactively extending the terms of any copyrights still in force. Following the enactment of the Copyright Term Extension Act in 1998, a coalition of plaintiffs led by publisher Eric Eldred argued that this act and a previous extension of the copyright term in the 1970s had created a "de facto" "perpetual copyright on the installment plan". This argument was rejected by the US Supreme Court in "Eldred v. Ashcroft", which held that there was no limit to how many times the term of copyright may be extended by Congress, so long as it is still a limited term at the time of each extension.