You need to check the terms of your lease. See if there is a restriction on a similar type business operating in the same strip center, etc. as the one in which your business is located. If there is, then your landlord is in breach of the lease and you can commence a civil suit to enforce the restriction. If not, then I'm afraid that your landlord is within its rights to allow a competitor to operate. While not good business since it can hurt one or both of the tenants, it is unfortunately legal.