HOUSTON, Texas — Houston ISD begins a new school year come Monday. But it will be without a full roster of teachers.

"We still have vacancies that we need to fill at our campus level,” said HISD Interim Superintendent Grenita Lathan.

Lathan told us administrators have a plan to help make sure every classroom is covered on the first day of school.

"And so we’re looking at that day by day, school by school, to ensure that we have certified teachers in all of our classrooms,” said Lathan.

RELATED: HISD hopes new tools cut back on transportation issues in the coming school year

RELATED: HISD given overall grade of 'B' by the state with 250 schools passing, 21 failing

The district isn’t explaining what that plan entails or exactly how many vacancies there are in a district that employs more than 11,000 teachers.

The Houston Federation of Teachers said the district needed more than 500 teachers at one point this summer.

It fears making up for them just means using substitutes or combining classrooms.

"Which is a disaster," said union vice president Andy Dewey. "Not only do you have one under-served classroom, then you have two, maybe even three.”

The union blames recruitment issues on below average salaries, compared to other districts, and what it calls a punitive teacher assessment system.

RELATED: Who owns the school supplies teachers are getting from #ClearTheList?

RELATED: Hard work finally pays off for HISD's Kashmere High School

However, the threat of the state taking over the HISD Board of Trustees is a more timely concern for a district the union says is, otherwise, well-run.

"Teachers want to move into the area, you want to get a home," said Dewey.  "Is your job going to be there next year?”

This year is what the superintendent said she’s focused on no matter the issues.

"Whatever happens, we stand prepared to serve children in HISD,” said Lathan.

Lathan said there’s an ongoing need for bus drivers as well.

The district plans to hold recruiting fairs to help address that.