Conservative groups push SCOTUS to tackle Washington state's capital gains tax

Conservative groups are making another push against Washington state's capital gains tax.

As of this year, the state taxes people for selling certain assets — such as stocks and bonds — worth more than a quarter of a million dollars.

RELATED: Seattle eyes capital gains tax of its own

The Freedom Foundation already took its appeal against the tax all the way to the U.S. Supreme Court.

This week, the Washington Policy Center, and a group of other conservative organizations, joined the case with a friend-of-the-court amicus brief. They're pushing for SCOTUS to take up the case.

The center is focusing on the constitutionality of the tax, arguing that Washington's aim to tax out-of-state transaction runs afoul of the Commerce Clause of the U.S. Constitution.

Washington's Supreme Court already upheld the state's capitol gains tax in March of this year.

According to a statement from the center:

The Washington Supreme Court’s decision threatens to unsettle numerous limitations on the scope of states’ taxing power and thereby prompt other states to follow Washington’s lead, when it suits their own purposes. If Washington can lay an excise on out-of-state sales of capital assets involving only out-of-state property, may California impose a gas tax on gasoline purchases in Arizona? May Texas impose an excise tax on stock sales in New York? May Pennsylvania impose a sales tax on grocery store checkouts in Ohio? Straightforward and long-standing principles of federalism dictate that the answer to all these questions should be no. But if this Court does not review Washington’s claimed authority to impose an excise tax with extraterritorial effect, other states will surely follow Washington’s lead and enact novel excise taxes of their own.

Other organizations that signed on to the amicus brief include: Americans for Tax Reform, California Policy Center, Grassroot Institute of Hawaii, Illinois Policy Institute, Independence Institute, National Taxpayers Union Foundation, Manhattan Institute for Policy Research, Mountain States Policy Center, Oklahoma State Chamber Research Foundation, Opportunity for All Coalition, Reason Foundation, and the Tax Foundation.