More than 45,000 Verizon workers were on strike for a second day Monday after negotiations broke down.

The strike is the first ever in the 11-year history of the second-largest U.S. phone carrier. The company has promised no service interruptions, saying that 40,000 managers, retirees, and contractors have been trained to fill the roles of union employees.

Verizon claimed that drastic cuts to worker benefits are necessary because of eroding profitability.

“It is clear that some of the existing contract provisions, negotiated initially when Verizon was under far less competitive pressure, are not in line with the economic realities of business today,” Verizon Chief Executive Officer Lowell McAdam said in a statement Sunday. “In fact, under these contracts, benefit costs have risen consistently even as the wireline business has shrunk.”

Communications Workers of America (CWA) and the International Brotherhood of Electrical Workers (IBEW) contend that Verizon had no intention of compromising when it entered into negotiations with the unions on June 22.