After the biennial 140-day regular session has expired, the Governor can call an unlimited number of special sessions. The governor decides what the legislature will work on during these special sessions.
Traditionally, governors called special sessions only during difficult times, like the budget crisis of the mid-1980s when world oil prices had plummeted. However, the mere threat of calling a special session often is enough to force the legislature to focus on the policy areas of greatest concern to the governor. Generally, legislators don't like to stay in Austin past the end of the regular session because of their part-time status. They have other jobs and careers, some in the far-flung reaches of the state, which they put on hold while in session.