The women were among a group of about 150 rallying in support of immigration reform.
The rally began at Downtown Park in Bellevue. Protesters then marched to the GOP headquarters, where a smaller group of about 40 entered the building and refused to leave.
Among those arrested inside the building were Peggy Lynch, wife of outgoing Seattle Mayor McGinn; the executive directors of 21 Progress, Casa Latina and the NW Network; the political director of SEIU Healthcare 1199 Northwest, and the presidents of the Washington Education Association and AFT Washington.
The woman said in a statement that they were demanding immediate action on a "comprehensive immigration law that treats women and children fairly."
The women were booked for first degree trespassing, then released, Bellevue police said.
The protest was one of 10 scheduled across the country in key Republican House member districts.
The head of the state Republican Party, Susan Hutchison, was out of town but said in a statement she agrees the immigration system needs to be reformed.
She says the demonstrators were arrested after refusing a request from the building landlord to leave. Hutchison says she's happy to have a dialogue, "but you cannot fix a broken law by breaking the law."