The Washington Post recently ran an article detailing the threat of deportation as an "abuser's weapon." (full story here). The Violence Against Women Act, however, is designed to combat this threat by providing visas to certain family members who are the victims of abuse. Abused spouses, children and parents of abused children are able to petition for visas. This is designed to help alleviate the pressure to remain in an abusive household due to fear of removal from the United States.
U Visas are similar in that they are designed to encourage undocumented residents to vocalize crimes of which they are aware. With U visas, however, undocumented residents are encouraged to provide information to law enforcement, assisting them in fighting crime.
Information on both VAWA and U Visas can be found in the resources section of this web-page under "special categories."