The pair were referred to the RFL Disciplinary Committee hearing on Tuesday evening after being charged by the RFL’s Match Review Panel.
Smith will face two charges from the Rhinos’ Engage Super League Round 11 fixture at Headingley Carnegie on Sunday, both involving illegal use of the knees in a tackle on Hull FC stand-off Jordan Turner and hooker Shaun Berrigan in the 11th minute.
The charge is a Grade A offence which carries a tariff of up to a one-match suspension if the player is found guilty. Any ban would rule Smith out of Leeds’s fourth round tie at Hull on Saturday.
Johnson has also been charged with a Grade A offence, a dangerous throw on Nick Scruton of Bradford Bulls in the Dragons’ home defeat last Saturday. Suspension would force Johnson to miss Catalans’ home fourth round tie against Salford.