WASHINGTON, May 20 — Employers, who helped shape a major immigration bill over the last three months, said today that they were unhappy with the result because it would not cure the severe labor shortages they foresee in the coming decade. In addition, employers expressed alarm as they learned that the Senate bill would require them to check a government database to verify that all current and former employees — aliens and citizens alike — are eligible to work in the United States. The Senate begins debating the bill on Monday. Supporters, including the White House, had hoped that senators...