Miami-Dade County, frustrated over what it asserts is an inability to get a straight answer, fired Deloitte Consulting LLP as its employee-benefits consultant Monday, alleging breach of contract. The spiraling dispute stems from Miami-Dade's request — amid heated labor contract negotiations — for a legal opinion from Deloitte on whether the county can, under federal tax law, offer to deduct 10% of employees' pay for healthcare premiums. The county needs clarification on the pretax health care deductions quickly, since it is pushing to have labor agreements with 10 unions by Nov. 1. The mayor has pledged to begin layoffs if agreements aren't in place by that deadline in order to ensure the county stays within budget. The county, which currently makes 5% pretax deductions from salaries for health-care coverage, wanted to offer unions the 10% pretax deduction as an alternative to pay cuts. In responding, Deloitte experts raised questions about whether the county has been properly following federal tax rules while making the 5% pretax deduction for health care -- in at least some cases.