It's not clear what specific topic Obama will tackle, but Trumka said his organization was working with the administration to plug holes in the Affordable Care Act.

“We have been working with the administration to find solutions to the inadvertent holes in the act,” Trumka said. “We are working to try solve problems, just like they tried to solve problems with employers, with large business and small business groups.”

Secretary of Labor Tom Perez and Sen. Elizabeth WarrenElizabeth Ann WarrenRising star Abrams advances in Georgia governor race Progressive rise is good news for Sanders, Warren Juan Williams: Trump gives life to the left MORE (D-Mass.) will also appear at the four-day AFL-CIO convention, the group said in a release.

The president's fundraiser that night will benefit the Democratic National Committee. 

Obama has been a prolific fundraiser in California since his reelection, traveling repeatedly there to raise cash for congressional Democrats. Before a summit with Chinese President Xi Jinping in late May, Obama appeared at events benefiting the Democratic Senatorial Campaign Committee and Democratic National Committee. In April, Obama and House Minority Leader Nancy Pelosi (R-Calif.) raised cash in the Bay Area for House Democrats.

At the time, White House press secretary Jay Carney defended the president's fundraising push as "a traditional exercise."

"I think it’s important to note that — because you’ve seen a lot of rhetoric from the other side suggesting that there is something wrong with that — that Republican leaders in the House and the Senate have been out raising money for Republican candidates; that this is a traditional exercise," Carney said.

- Kevin Bogardus contributed. 

An earlier version of this post included incorrect information. This post was corrected at 11:39 a.m.