About 2,000 workers at Johns Hopkins Hospital have threatened to strike if the hospital does not agree to a wage increase of as much as 40 percent for some employees. A union representing the hospital's service and maintenance workers, including housekeepers and those who deliver food to patients, requested the increase because it said many of the workers rely on government assistance programs such as food stamps and Medicaid to support their families. The contract with the workers, members of labor union 1199SEIU United Healthcare Workers East, was set to expire at midnight Monday, and the two sides continued to negotiate late into the evening but no agreement was reached.