A strike that could have halted production of some of General Motors' most profitable and important vehicles was narrowly averted Thursday.

About 15 minutes before a 10 a.m. strike deadline, GM and the UAW reached a tentative agreement for a new contract for about 600 of GM's Subsystems Manufacturing LLC employees.

The details of that agreement are not yet known.

"The UAW will now focus on the ratification process," GM spokesman Dan Flores said in a statement. "We won’t be discussing details of the tentative agreement until the ratification process is complete."

The subsystem employees have a different contract than that of the 48,000 GM hourly workforce in the U.S. that went on strike in 2019.

The subsystem workforce's contract expired 14 months ago and after repeatedly failing to reach an agreement on a new contract, the UAW set a strike deadline for 10 a.m. Thursday for the subsystem workers at Flint Assembly, Factory Zero, Lansing Grand River and Orion Assembly plants.

The UAW confirmed that it and GM Subsystems Manufacturing LLC have reached a tentative agreement that the union will show to members of Locals 22, 598, 652 and 5960.

“This negotiation was drawn out and hard fought,” said UAW Vice President Terry Dittes, who is director of the union’s General Motors Department, in a statement. “We look forward to presenting the tentative agreement to members for their ratification.”

Critical to GM production

The subsystem workers' strike could have brought production of GM's most profitable vehicles to a standstill within hours.

Subsystem workers sort all the parts that come into to the plants and then deliver those parts to the assembly line to keep production humming.

"They bring me my parts. I can't do my job on the line without them bringing me the parts," said a GM hourly worker at Flint Assembly plant. The worker declined to be named because of the sensitive nature of contract negotiations.

Flint Assembly is where GM builds its highly profitable and popular Chevy Silverado and GMC Sierra heavy-duty pickups.

Local 598 Shop Chairman Eric Welter put out memos to union members at Flint Assembly earlier this week, the person said. The memos emphasized that GM's regular hourly workers must — under terms of their 2019 National Agreement — cross the subsystem workers’ picket line and report to work if there is a strike. GM hourly workers could be fired if they joined the picket.

The worker told the Free Press that Welter said in the memo that Flint Assembly could “probably make it to the end of the first shift” before it had to stop production without subsystem workers there to sort and deliver parts to the line. First shift runs from 7 a.m. to 3 p.m.

Welter did not return calls for comment.

Impact EV launches

At Factory Zero in Detroit and Hamtramck, GM has been building its 2022 GMC Hummer EV pickup, a new EV that is crucial to GM's segue to go all-electric by 2035. There are about 220 subsystem workers there.

The plant is shut down until July 25 as GM upgrades it to build future EVs such as the Hummer SUV next and then the 2024 Chevrolet Silverado EV and the Cruise Origin self-driving EV.

About 350 hourly workers are temporarily laid off there, but 100 skilled trades employees continue to work, said shop chairman Scott Harwick of UAW Local 22, which represents hourly workers at Factory Zero.

Harwick told the Free Press a strike by the subsystem workforce could have hurt GM’s preparation to start production of the Hummer SUV.

“Those pre-production vehicles, there’s only so much stock on the line now,” Harwick said. “I’m not sure how long they could keep going."

The two other plants with subsystem workers impacted are:

• Lansing Grand River Assembly, represented by Local 652 where GM builds Cadillac CT4, Cadillac CT4-V, Cadillac CT5, Cadillac CT5-V and Chevrolet Camaro.

• Orion Assembly plant in Orion Township, represented by Local 5960, which makes the Chevrolet Bolt EV and Bolt EUV.

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Contact Jamie L. LaReau: 313-222-2149 or jlareau@freepress.com. Follow her on Twitter @jlareauan. Read more on General Motors and sign up for our autos newsletter. Become a subscriber.

This article originally appeared on Detroit Free Press: GM, UAW get tentative agreement for Subsystem's Manufacturing workers