  Let $\ell \geq 5$ be a prime and let $N$ be a square-free integer prime to
$\ell$. For each prime $p$ dividing $N$, let $a_p$ be either $1$ or $-1$. We
give sufficient criteria for the existence of a newform $f$ of weight 2 for
$\Gamma_0(N)$ such that the mod $\ell$ Galois representation attached to $f$ is
reducible and $U_p f = a_p f$ for primes $p$ dividing $N$. The main techniques
used are level raising methods based on an exact sequence due to Ribet.
