London - Manchester City have written to the body in charge of professional referees to raise their concerns over a series of dangerous challenges suffered by their players, according to widespread reports on Saturday.
The BBC reported the Premier League leaders have cited nine challenges they feel have not been sufficiently punished by referees in recent months to Professional Game Match Officials Limited (PGMOL).
City would also like to see a change in Football Association rules that would allow incidents seen by referees on the field to be reviewed again retrospectively.
That could possibly mean yellow cards being upgraded to red if evidence was sufficient.
In one of the worst challenges a fortnight ago, winger Leroy Sane was ruled out for six weeks by ankle ligament damage suffered after being caught late by Cardiff's Joe Bennett.
"I said many times the only thing they (referees) have to do is protect the players," City boss Pep Guardiola said after his side's 2-0 FA Cup fourth round win in the Welsh capital.
"For the football in general, and for the players who are the artists, they must do that. That's why we are all here."
Bennett received only a yellow card, as did West Brom's Matt Phillips for a high tackle on Brahim Diaz three days later.
Other bad challenges which have sparked controversy include lunges on Kevin De Bruyne by Crystal Palace's Jason Puncheon and Tottenham's Dele Alli and James McClean of West Brom.
In a much-criticised move, Guardiola named only six substitutes for last weekend's 1-1 draw at Burnley claiming he had no more players left due to a spiralling injury crisis.