Updated at 4:30 p.m. Friday with statement from association president. 

Dallas officers will not be allowed to request any more time off during the trial of fired police officer Amber Guyger.

Charged with murder in the shooting death of Botham Jean, Guyger's trial starts on Sept. 23.

Guyger shot and killed Jean in his own apartment on Sept. 6, 2018. 

Off-duty but still in her uniform, Guyger said she walked into an apartment she believed was her own and shot Jean, believing he was a burglar. 

RELATED: Dallas County judge hears requests regarding witnesses, evidence in Amber Guyger's pre-trial hearing

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In two separate memos, officers were told they will not be granted time off from the start of the trial through at least Oct. 7.

Detectives were also told to have their uniforms, gas masks, helmets and other gear ready.

Terrance Hopkins, president of the Black Police Association of Greater Dallas, said the practice is common when there is high demand for officers. 

"The move is to make sure the city has enough resources to protect it," Hopkins said. 

Officers already scheduled off during that period will still be allowed to take the time off, Hopkins said. 

More on WFAA: 

Full coverage of Botham Jean shooting