The security contractor at Xcel Energy’s Monticello nuclear power plant appears set to lock out some guards after a breakdown in contract negotiations.

The lockout would affect “lieutenants” or “shift leaders,” whose contract expires at midnight Saturday, said Josh Haider, head of United Security Professionals Local 2. There are about 25 unionized lieutenants at the Monticello plant employed by G4S, a large global-security firm.

G4S and Xcel have been training replacements for union guards over the past month, Haider said.

Local 2’s primary concern is a G4S plan to move to a new health plan and cut its contributions to guards’ health care premiums by nearly 50% or $10,000 per worker annually, Haider said. “We would get a significantly worse health plan.”

G4S, which is based in London, did not respond when asked for comments.

Minneapolis-based Xcel said in a statement it provides training for all security contractors at its properties, a common power-industry practice. “Because we are responsible for ensuring security staff are fully trained and prepared, we chose to provide the training directly.”

Xcel, Minnesota’s largest electricity provider, said it has “taken steps to ensure” that negotiations between G4S and Monticello guards don’t affect the plant’s security, safety and operation.

That includes building a separate entrance gate for G4S workers, apart from an entry for Xcel’s employees and guests.

Xcel’s many unionized workers then wouldn’t have to cross any picket lines set up by locked-out guards.

Local 2 is one of two union locals of the independent United Security Professionals, which together represent around 120 guards at the Monticello nuclear plant. The majority of guards at Xcel’s Prairie Island nuclear power plant are represented by a different union.

Local 2’s contract expired in January and since has been extended twice. The current extension expires at midnight Saturday.

Haider said Local 2 members have voted down three G4S contract proposals. The union last submitted a proposal 10 days ago, cutting its wage-increase demands to 2.5% per year, but not moving on health care; it was rejected, Haider said.

Local 2’s contract is the only contract for G4S nuclear plant guards in Minnesota that has come up for negotiation this year. The contract for Local 1, which represents “officers” at Monticello, expires at the end of December.

G4S took over Xcel’s nuclear-plant security earlier this year. Before G4S, Securitas held Xcel’s nuclear security contract for five years. Securitas had taken over the job from G4S.