Lancaster, who took interim charge of England prior to the RBS 6 Nations, picked his first squad since being named permanent boss when he revealed a 42-strong group for the tour of South Africa.
Among those selected was hooker Dylan Hartley, who received an eight-week ban during the Six Nations for biting Ireland's Stephen Ferris.
And despite calling the Northampton captain into his squad, Lancaster insists he will remind Hartley of his responsibilities and point out to the rest of the squad the danger of conceding cheap penalties.
"If we can't trust a player on the field then he won't be selected. We will have a pretty strong conversation and he has to prove to us he is ready to come back into the Test arena," he said.
"Attitude, energy, emotion and discipline should be a given for an England team now.
"We work very hard on our on-field and off-field discipline. What we will have to reduce is our penalty count. That is not just Dylan.
"We can't be giving penalties away and being indisciplined on the field, particularly with Morne Steyn who can kick them from anywhere.
"We are confident the messages we are giving the players are being received. We will make sure Dylan gets that message."