It comes after the announcement that winger Jadon Sancho will train away from the first team until issues with the manager are resolved.
Ten Hag opted not to talk about Sancho on Friday and did not say how long he would remain away from the first team.
“It is my job to control the standards,” Ten Hag said.
“Strict lines is what the club asked me because there was no good culture before I entered last season.
“Of course, it is never someone only makes one mistake, it is a whole process before you come to a certain outcome about strict lines.
“If staff or players or whoever, there is a structure to cross lines so you have to be strong.”
Manager Ten Hag took charge at United ahead of last season.
He left Sancho out of his squad for the loss at Arsenal earlier this month, saying the England international's training performances had been below standard.
The 23-year-old Sancho rejected the Dutchman's reasoning and claimed he had been “a scapegoat for a long time”.
United are also missing Antony after the winger agreed to delay his return from international duty “to address allegations” of assault made against him.
Antony, who denies the allegations, had been due back to training on Monday after being dropped from Brazil's squad for their World Cup qualifiers against Bolivia and Peru, and Ten Hag says he has “no idea” when the former Ajax player will return.
However, Ten Hag said the remainder of the squad were in “good spirits”.
“You have sometimes setbacks in seasons, players are injured or for other reasons are not available so you construct a squad,” he added.
“The squad is very good and the players who are available are motivated to give a good performance.”
Maguire abuse ‘disrespectful'
Ten Hag said the abuse directed towards defender Harry Maguire from fans has been “disrespectful”.
Maguire, 30, lost his place in United's starting line-up along with the captaincy this summer, but he continues to be selected for England.
After coming on for the second half of the friendly against Scotland on Tuesday, he scored an own goal and was mocked by the home fans as England won 3-1.
“I have said many times, it is disrespectful, [he] doesn't deserve it,” Ten Hag said.
“He is a great player, gives great performances. It is crazy but how it works. Harry has to block this.”