Section 3 of the federal Copyright Act states copyright is the sole right to produce or reproduce the work, or any substantial part of the work, in any material form. Section 27(1) defines copyright infringement: to do anything, without the owner’s consent, that only the copyright owner has the right to do. Section 27(2) adds that to distribute a work to such an extent as to affect prejudicially the owner of the copyright owner is also infringement. Putting these concepts together, assuming a substantial part of your work is being used/reproduced/distributed, then your work is infringed and you have the basis to take action. The usual first step is to send a cease-and-desist demand letter. Such letters often work because many infringers are ignorant of copyright law and will cease when informed. If not, then you may elect to commence a lawsuit for copyright infringement. If you have registered copyright in your work before the infringement, the legal action will be simpler. To prove infringement, the plaintiff must show both similarity between the infringed work and the infringing work, and access (for example, the infringer had access to the infringed work).