Forty students have been suspended at a £20 million city academy since it opened two weeks ago.
Paul Prest, chief executive of Academy 360 in Pennywell, Sunderland, said he imposed the disciplinary crackdown so that "no student is left in any doubt as to what is expected of them".
But the National Union of Teachers (NUT) said the suspensions seemed "excessive".
The students, suspended for a variety of behavioural reasons, have been given work packs to complete before returning to school - with threats of further suspension if they fail to do so.
Other measures introduced at the flagship academy, which is sponsored by housing group Gentoo, include an automatic exclusion for students caught smoking and a ban on leaving school grounds at break times and at lunch.
There is also a stock of spare uniforms to loan to pupils who do not come properly dressed for school.
Mr Prest told the Sunderland Echo: "Academy 360 is committed to providing all of its students with the best possible education.
"To secure that, it is vital that we set and achieve the highest standards - in work, behaviour and discipline - and we cannot tolerate any attempt to subvert those standards."
Elaine Kay, northern regional secretary for the NUT, said she was not surprised by the measures.
"That tends to be the way we find academies working. They take over schools in challenging areas and remove the pupils who aren't going to enhance their standing and image, and they expect the authorities to place them somewhere else."
She said that while these suspensions were only short-term, and she did not expect schools to tolerate bad behaviour, "it seems this academy is following a similar line to other academies".
"It seems rather excessive at this early stage to have 40 suspensions."
Pupils at the academy have also expressed concern about the new regime, with several writing to their local paper to complain about not being allowed out during their lunch break, which has been reduced to 30 minutes.
But a spokeswoman for the academy said: "The response has been overwhelmingly positive in the community, because litter and disruption problems have been improved."
She added: "Staff are over the moon to see disruptive behaviour being dealt with properly for the first time."
The academy, which replaced Pennywell School and Quarry View Primary School, was the first to be developed under Sunderland City Council's Building Schools for the Future programme.