"Christians are upset with Starbucks for turning against God...Starbucks can follow Satan if they want to," Steven Andrew, and evangelical pastor and president of the USA Christian Ministries in California, said in a statement. "However, pastors are to help Christians. Are you on the Lord's side? Will you help the USA be blessed by God?"
The call for the boycott was released Tuesday, a day prior to the bill's passage in Washington's State Senate Wednesday night, according to Reuters.
USA Ministries is also asking for Christians to stop serving the brand at their church facilities and events.
The Seattle-based coffee chain joined more than 100 other firms in backing the same-sex marriage bill.
Other companies taking a similar position include Nike, Google and Microsoft, Half Moon Bay Patch notes.
If the bill passes in the state house of representatives next week, Washington will become the seventh U.S. state to recognize same-sex unions.