Washington (CNN) Labor unions are launching a new advertising campaign prodding Democratic lawmakers to break with President Barack Obama on free trade.

The AFL-CIO will meet the introduction of a bill to fast-track Pacific Rim and European pacts with a six-figure online and radio advertising campaign targeting 16 Democrats in the Senate and 36 in the House, the group told CNN.

That campaign, which raises the specter of job losses, unregulated chemicals in foods and more, is set to run through August and could expand to include television spots.

"These ads -- which follow months of rallies, congressional meetings and unprecedented grassroots activities -- will remind politicians that the trade debate is enormously important to working families," AFL-CIO President Richard Trumka said.

Labor is targeting a bill that Senate Finance Chairman Orrin Hatch and top-ranking Democrat Ron Wyden have said they expect to introduce at any moment.

"We have seen too often how bad trade deals have devastated our communities. We can't afford to pass fast track, which would lead to more lost jobs and lower wages," Trumka said. "We want Congress to keep its leverage over trade negotiations -- not rubber stamp a deal that delivers profits for global corporations, but not good jobs for working people."

The AFL-CIO's ad campaign comes weeks after the group said it was shutting off political donations to Democratic candidates to save up for a trade battle royale, led on the left by Massachusetts Sen. Elizabeth Warren, against Obama.

It's also a preview of what could become one of the most challenging issues for Hillary Clinton to navigate during the Democratic presidential primary. As Obama's secretary of state, she praised the trade talks that liberals are now set on thwarting. Liberal challengers like Vermont Sen. Bernie Sanders and Maryland Gov. Martin O'Malley have signaled they'll try to force Clinton's hand on the issue.

The ads come while Obama's administration is close to finalizing one of the biggest trade deals in history: the Trans-Pacific Partnership. It includes all of North America, as well as Asia-Pacific countries like Australia and Japan -- the deal's real jewel in American exporters' eyes.

On that deal's heels is a similar one to smooth out regulatory differences between the United States and the European Union.

The "fast-track" bill -- which would allow the Obama administration to submit those deals to Congress for up-or-down votes with limited debate and no amendments -- is a cornerstone to those efforts.

Trade negotiators say it's impossible to convince foreign leaders to take their own political risks and strike a final agreement if they're concerned Congress would just re-open the agreement later.

That also means, though, that liberal opponents of Obama's trade efforts can focus their opposition on defeating the fast-track bill, rather than debating the merits of the finalized trade deals.

They'll be backed by a handful of conservatives who say they don't trust Obama enough to hand him fast-track authority and don't want to give him a legacy-making victory in his final two years in office.

Obama administration officials, led by U.S. Trade Representative Michael Froman, have argued that the left should embrace their trade efforts. They say the trade deals are Democrats' best chance of righting the problems they've identified with previous trade deals and lifting international standards on areas like labor rights and environmental protections.

They've also pointed out that U.S. exports support 11 million jobs and have accounted for one-third of the country's economic growth since 2009.

"To unlock 21st century economic opportunities for the American people, the Obama administration is fighting to complete groundbreaking new trade agreements with the Asia-Pacific and with Europe that put Main Street and the American middle class first," Froman's office said in a memo Wednesday.