A high-profile senator appointed by Prime Minister Justin Trudeau is joining a growing group of senators calling on Don Meredith to resign from the upper chamber over his sexual relationship with a 16-year-old.

In a letter to Meredith and copied to every senator, Andre Pratte writes that people will forgive Meredith if admits his mistakes, but that still won't render him fit to serve in the Senate.

Meredith's conduct as a senator and as a man was unconscionable, Pratte says in the letter sent Sunday.

He urges Meredith to resign so the Senate's reputation does not suffer more than it already has.

The details of the relationship and Meredith's conduct were outlined in a damning report from the Senate ethics officer last week that said Meredith had sexual relations with the woman once before she turned 18 and twice after she turned 18 and also had explicit online chats with her.

Meredith acknowledged in the report that he had sexual relations with the woman, but only after she turned 18.

Ethics officer Lyse Ricard ruled that Meredith used his position as senator improperly and that he violated the Senate's ethics code.