Federal authorities said Tuesday a Texas couple forced a Nigerian woman to work for them without pay during a two-year period in which she was physically and verbally abused, made to work nearly 20 hours per day and told to sleep on the floor.

The 38-year-old nanny, whose name wasn’t revealed in the criminal complaint, told investigators she was promised $100 per month to work at the home in Cinco Ranch but was never paid. Chudy and Sandra Nsobundu allegedly held the woman hostage, taking away her passport so she was unable to leave the country.

"She regularly endured physical and verbal abuse and was not treated like a human being," the criminal complaint said.

According to The Houston Chronicle, the woman is not married and has no children. She also wasn’t allowed to talk to her family members, according to the complaint.

The Nsobundus were arrested Monday on charges of forced labor, withholding documents, conspiracy to harbor an illegal immigrant and visa fraud. Sandra Nsobundu, 50, was granted an unsecured bond and Chudy Nsobundu, 56, was granted a $5,000 bond.

The couple faces up to 20 years in prison if convicted.

Ruben Perez, one of the federal prosecutors handling the case, said after Sandra Nsobundu's hearing that the nanny was "enslaved" by her employers. Perez said cases in which immigrants and others are forced to work in homes in harsh conditions as nannies or caretakers are more common than people think.

"We know they are out there. When it comes to our attention we'll act on them," he said.

The nanny was living in Lagos, Nigeria before she started to live with the Nsobundus in September 2013. The Nsobundus are naturalized U.S. citizens originally from Nigeria. The complaint said the nanny would work every day from 5:30 a.m. to 1 a.m., couldn't take breaks and had to eat leftovers and not fresh food, including being forced to only drink milk left in bowls in which the children had eaten cereal. She also couldn't take hot showers, according to the complaint.

The nanny alleged Sandra Nsobundu repeatedly hit her if she thought the woman wasn't doing her job correctly. The complaint said Sandra Nsobundu is accused of once striking the nanny across the face with a slipper and threatening to "shoot her and kill her" after not liking the socks the woman had put on one of the younger children.

After the nanny found out that she hadn't been paid in two years, she reached out for help and was rescued last October following a tip to the National Human Trafficking Resource Center, the complaint said. It's not clear who made the tip.

The Associated Press contributed to this report.