We consider the existence of power integral bases in
composites of polynomial orders of number fields.
We prove that if the degree of the composite field
equals the product of the degrees of its subfields and
the minimal polynomials of the generating elements of the
polynomial orders have a multiple linear factor in their
factorization modulo q, then the composite order admits no power integral
bases. As an application we provide several examples including
a parametric family of "simplest sextic fields.''