Is it permissible for the Imam to say, "Send prayers upon the Prophet," during the Friday sermon?

It is permissible for the preacher to address the congregants with phrases such as "Remember Allah" or "Invoke blessings upon the Prophet" if there is a need for it, such as the congregants falling short in invoking blessings upon the Prophet, or to alert them to an important matter, or to awaken them from heedlessness. However, to do so excessively without justification or to make it a continuous habit is contrary to the Sunnah.