The International Brotherhood of Electrical Workers and SBC have met around the clock this week to try to resolve differences over health care costs and job security.
About 11,500 SBC workers could go on strike at midnight Saturday if a new contract agreement isn't reached.
The IBEW represents technicians, customer service representatives and sales people, with most in Illinois. It has the third-most phone lines of the 13 states SBC serves.
The Communications Workers of America reached a tentative deal with SBC last month after a four-day walkout. The CWA represents more than 100,000 SBC workers.