The city of Houston is gearing up to play hardball with its firefighters union in advance of contract mediation by passing less favorable employment terms that would take effect if the firefighters' current agreement lapses next week. The changes subject to City Council approval Wednesday would come a month after the fire union declared an impasse in negotiations with the city. Firefighters' last contract expired three years ago, and they have been operating under "evergreen" terms since, which has meant forgoing raises in exchange for fewer restrictions on time off. That arrangement expires June 30, at which point firefighters' employment terms would revert to those detailed in city ordinance unless mediation talks set to begin Thursday produce a deal first.