Pepco and its employees union are heading back to the bargaining table after the union rejected the company's "last, best and final" offer by a 5-to-1 margin.

The International Brotherhood of Electrical Workers opposes Pepco's proposal to staff up to 20 percent of its call center with part-time employees and to change the way the union bargains over health benefits.

"The company wants to basically take over health and welfare without any negotiations with us," said IBEW Local 1900 President Jim Griffin. "They would have the right to make changes to what's covered and what's not covered without our involvement."

But Pepco spokeswoman Myra Oppel called the union's health care concerns "a red herring."

"In over 30 years, there has not been a grievance or an arbitration over health benefits," she said.

Though the sides are scheduled to return to the bargaining table Friday afternoon, Oppel said Pepco won't offer more money, "regardless of the outcome."

Pepco also says the union lost the opportunity to apply the new, higher wages retroactively to June when it failed to approve a contract by the end of Thursday.

Griffin said his members aren't worried by either threat.

The union's original contract was extended until Sept. 16. Now that the extension has run out, the union can declare a strike with 48 hours' notice.

Pepco has been preparing for a strike by training management employees to assume union members' jobs, Oppel said. The company also would rely heavily on contractors.

"If necessary, we could scale back some of our reliability work," she said.

But a strike could hurt service, which is already heavily criticized, public officials warn.

"They're starting from a pretty low base, and ... when they take the workers off the job, it's only going to get worse," said Maryland state Sen. Brian Frosh, D-Montgomery County. "Maybe they can pull it together with chewing gum and rubber bands for a few days or maybe even a week or two, but [the union has] real experts who can do the job, who have been trained to do the job."

The dispute is also damaging the already low public opinion of the company named the most hated in America last year.

"Despite probably spending millions and millions of dollars in advertising ... they don't understand how they renew good faith with the public," said D.C. Councilwoman Mary Cheh, D-Ward 3. "They renew good faith with the public by treating their customers well and treating their employees well."