SAN JUAN, Puerto Rico (AP) _ Telephone workers called a strike for Thursday to protest the $1.9 billion sale of a controlling stake in the state-owned telephone company.

The walkout coincides with an expected vote by Puerto Rico's Senate to approve the sale, in which a consortium led by GTE Corp. will obtain 50 percent plus one share of the Puerto Rico Telephone Company.

``It's certain. Tomorrow we begin the strike,'' said Jose Juan Hernandez, president of the 4,247-member Independent Telephone Employees Union.

The Independent Brotherhood of Telephone Employees, with 2,000 members, has also voted to strike. Other public sector unions were expected to join the protest.

While GTE has pledged no immediate layoffs, labor leaders fear job losses among the telephone company's 8,000 employees. They also complain that Puerto Rico's government struck a poor bargain in secret negotiations.

The Puerto Rico Telephone Company has hired three security guard firms to protect employees who continue working, company president Carmen Ana Culpeper said Wednesday.

She also warned that lines might be sabotaged.

``The network is huge and unfortunately, many of the employees know where to cut it,'' Culpeper said. ``We cannot guarantee that nothing is going to happen.''

During a work stoppage in October, hundreds of customers on the island temporarily lost telephone service because of severed fiber-optic cables.