The European parliament will vote on whether Bulgaria and Romania can join the region's free travel zone, known as the Schengen agreement, this week.
The agreement allows people from member countries to travel without the need for any sort of visa.
In return for open borders in Europe, the European Union is demanding that Bulgaria makes it very difficult for people to immigrate from countries to its east like Turkey.
There's equipment that can tell if anyone is trying to breath in the back of a truck or to check for someone's heartbeat through metal walls
The strict measures have also led to the creation of Bulgarian migrant detention centres, designed to look like fortresses.
A group of detained Afghan women told Al Jazeera that they have put themselves and their children on a hunger strike against the inhumane conditions at the detention centre.
One of them said, "We want freedom. Our children haven't eaten for three days. We want to know what our fate is. We don't understand what will happen to us. This is torture. What have we done to deserve this?"
Al Jazeera's Laurence Lee reports from a detention centre in the first of our special series on European border controls.
Source: Al Jazeera