"The NZPFU does not support the lifting of the ban as it is not in the interests of your health and safety," national secretary Wattie Watson said in a notice to union members on Thursday.
"The NZPFU recommends members refuse to undertake pressure hose testing until the investigation is complete and any recommendations considered."
Watson told the Herald the union had not been told why the ban was lifted before the investigation was complete.
"Our position is to maintain that safety is paramount, and there is no reason to believe they should commence pressure hose testing at this point."
A notice had been sent out with some requirements for firefighters to follow procedures that would minimise the risk, she said.
Pressure testing a hose is routine after firefighters return from a fire job, to check hoses are working as they should be and don't have kinks or holes.
Without pressure testing, the hoses become a safety risk. However, Watson said there were enough hoses to keep using fresh ones until the investigation was complete.
FENZ national operations manager Paul Turner said a hose burst last month while it was being pressure tested, resulting in a firefighter sustaining a serious injury.
"Our thoughts are with the injured firefighter and we wish them a speedy recovery.
"The safety of our people is paramount. Immediately following the incident, we put a temporary ban on pressure testing all hoses while we undertook a formal investigation to work out why this happened and what we could do to prevent a similar incident happening in the future.
"This investigation has been undertaken in consultation with the Union and WorkSafe."
Turner said though the investigation was ongoing, preliminary findings had indicated
putting additional safety measures in place meant firefighters could resume pressure testing hoses.
These included:
• Ensuring people maintained a safe distance of at least 10 metres from the hose while testing it;
• Making sure the hose was laid in a straight line and that after testing, pressure was released at the pump before anyone approached it.
"In addition, we have also reminded everyone to ensure they are familiar with our procedures for pressure testing hose," Turner said.
Additional reporting: Dubby Henry