Section 724.011 of the Texas State Transportation Code states that anyone who is arrested for Texas DWI:
"is deemed to have consented, subject to this chapter, to submit to the taking of one or more specimens of the person's breath or blood for analysis to determine the alcohol concentration or the presence in the person's body of a controlled substance, drug, dangerous drug, or other substance."
This is known as "Implied Consent", and as mentioned earlier it essentially means that by the mere act of accepting a Texas State driver's license you have automatically consented to take a blood alcohol level test if the police deem it necessary.
Based on the implied consent clause, Texas (and many other states) have begun implementing what are known as "No Refusal" weekends. This program is a law enforcement strategy that allows jurisdictions to obtain search warrants for blood samples from any drivers who are suspected to be impaired but refuse roadside breath or blood tests. During these events, usually scheduled around holidays such as Labor Day or New Year's Eve the police, prosecutors and judges streamline the warrant acquisition process in order to obtain blood draw warrants.
During these "No Refusal" events the District Attorney’s Office usually stations staff members at centralized locations in order to immediately consult with the arresting officer. They collect the probable cause information used in the arrest and rubberstamp a warrant which is immediately faxed to a waiting judge. If there is any probable cause that warrant will be signed and returned, the suspect is taken to an on-site blood draw room and a nurse or phlebotomist will draw the suspect’s blood. If the suspect is uncooperative or combatant, officers will restrain the suspect while the blood draw is occurring.