Fort Worth Fire Chief Jim Davis has announced his resignation, just weeks after being put on paid administrative leave.

Numerous sources told CBS News Texas the decision came after the city's firefighters association threatened to take a vote of no confidence in his leadership, sources told CBS News Texas.

Raymond Hill, previously assistant chief, is serving as interim chief while the city's investigation continues.

Sources within the Fort Worth Fire Department told CBS News Texas that the Fort Worth Professional Firefighters Association's concerns included how the MedStar integration into the department was handled. One source called the process rushed, saying, "We made it happen, but it wasn't easy."

MedStar is the emergency medical services provider for Fort Worth and surrounding communities, responsible for handling the city's ambulance and paramedic operations.

Fire department sources also said tensions escalated after Davis announced in late August that all firefighters would be required to train as drivers to serve on ambulances. Members of the association have pushed to keep their firefighting duties separate from medical services.

Experts outside the department noted that assigning firefighters to ambulance duty significantly increases their workload. A spokesman for the fire department said the agency's medical division handles between 500 and 600 calls per day. On Oct. 15, the combined department responded to 576 calls, another spokesman said.

At the time Davis was placed on leave, the city said the investigation would take a few weeks. When contacted by phone, Davis told CBS News Texas he was deferring questions to his attorney, Stephen Kennedy, who said he hoped to have a statement later today.

The city declined to comment, and the firefighters association has not issued a formal statement, saying it wanted to let the process "work itself out."

Davis was sworn in as Fort Worth fire chief in October 2018. He previously served in the Columbus Division of Fire, in Ohio, where he oversaw training and education for the department.

Fort Worth fire chief resigns after complaints from firefighters association