It's up to the each employer. They can't just start making group heath premium deductions pre-tax though. They must put a Plan Document in place that complies with 125B legislation and file that with the DOL and the IRS first. Once that's done, then premium deductions can start being withheld on a pre-tax basis. The employer must also then comply with all the requirements of that section of the tax code regarding the deductions and when and why changes can be made.