The political network backed by billionaires Charles and David Koch said Monday it’s planning a “multi-year, multi-million-dollar” campaign to promote free trade and oppose President Donald Trump’s moves to impose tariffs on billions of dollars worth of imports.

The effort will include advertising, voter mobilization and lobbying in an attempt to “transform the way Washington and the rest of the country consider and value trade with other nations,” according to a joint statement from three Koch groups.

The network, the most influential conservative entity outside the Republican Party, has clashed with Trump before on trade and immigration. The Koch brothers, who each have a net worth of about $47 billion in the Bloomberg Billionaires Index, didn’t support him in the 2016 campaign but have since praised his efforts to cut taxes and regulations.

“The Trump administration has taken some incredibly positive steps for the American economy, but tariffs will undercut that progress and needlessly hamstring our full economic potential,” Tim Phillips, president of the Koch-affiliated Americans for Prosperity, said in a statement. “There are better ways to negotiate trade deals than by punishing American consumers and businesses with higher costs.”

Besides AFP, other Koch network entities involved in the project include the Freedom Partners Chamber of Commerce, the hub organization for top Koch donors, and the LIBRE Initiative, which seeks to woo Latinos to conservatism.

With a trade war brewing after Trump’s proposed tariffs on products from China and duties on steel and aluminum imports, the Koch network also released a list of trade principles and policy recommendations that its campaign will seek to advance.

Manufacturers and business groups, including the U.S. Chamber of Commerce, have slammed Trump’s decision last week to impose tariffs on steel and aluminum imports from the European Union, Canada and Mexico, warning that retaliation is likely and calling the move a tax on U.S. companies and consumers.

The Koch network isn’t expected to start the paid advertising related to tariffs until later in the summer, although Americans for Prosperity is already one of the nation’s most active television advertisers in this year’s midterm congressional campaign.

Keeping the Koch brothers and their donors happy is important for Republicans in an election year, especially as Democrats show signs of momentum as they campaign to win the 23 seats they need to gain control of the House after the November election.

The network, which could make a difference in some of the states that could tip the balance of power on Capitol Hill, plans to spend roughly $400 million on state and federal policy and politics during the two-year election cycle that culminates with the November balloting. That marks about a 60 percent increase over 2015-16, although leaders have said more than a third of the 2017-18 total has already been spent.