PPTA president Angela Roberts said it seemed that agreement had now been undermined.
The union understands the government has introduced a supplementary order paper to the Education Legislation Bill, which is currently being considered by the education select committee.
The PPTA understands it would change the proposed legislation to create a separate employment process for student teachers, meaning positions would not need to be advertised.
"The agreement we reached with the Ministry, Teach First and Auckland University resolved the situation satisfactorily for all the parties, or so we understood at the time" Ms Roberts said.
"Now the Minister is cutting right across the agreement we reached earlier this year. Not only is there no good faith in this action, she is actually undermining the Teach First programme by clumsily offering them preferential legal status that they do not need.
"There are some real risks involved in changing the law around appointments to schools - anything which weakens the transparency and fair process requirements would have to be done very carefully and with a very good rationale. We would be keen to be able to submit on this, as would many others in the sector."
A spokeswoman for Education Minister Hekia Parata said she was unable to comment on the matter as it was before the select committee, and to do so would be a breach of privilege.