The U.S. Senate on Thursday passed a spending bill with an attachment urging the State Department to do more to make Japan address its forced mobilization of women as sex slaves for soldiers during World War II.
The House of Representatives had already passed the bill for 2014 on Wednesday.
The attachment notes House Resolution 121 of 2007 and "urges the secretary of state to encourage the government of Japan to address the issues raised in the resolution."
The attachment is non-binding but has symbolic significance in pressuring Japan to apologize for the atrocities committed against the women, who mostly came from Korea.
President Barack Obama signed the bill into effect on Friday.
Representative Steve Israel, who spearheaded the attachment along with Representative Mike Honda, a third-generation Japanese American, in a statement urged Japan to "acknowledge and apologize" for the atrocities.
The 2007 resolution calls on the Japanese government to admit and officially apologize for the atrocity.