The president was spending Monday's holiday at a picnic with members of one of the largest construction unions, the United Brotherhood of Carpenters and Joiners of America.
Despite the focus on a possible U.S. attack on Iraq, Mr. Bush's Labor Day message would be about butter rather than guns, according to a preview from a senior administration official.
"The focus will be on strengthening our economy and economic security," he said.
Neither the war on terrorism nor Bush's determination to oust Iraqi President Saddam Hussein over Baghdad's alleged pursuit of weapons of mass destruction is expected to be a big factor in the Nov. 5 congressional races.
The trip was Mr. Bush's 13th as president to Pennsylvania, which has the fifth most electoral votes. He lost the state to Democrat Al Gore in 2000 and since has visited it more than any other.
Labor groups are key donors and organizers for Democrats, who cling to a one-seat majority in the Senate and are a handful of seats away from controlling the House. Thirty-six governorships also are at stake in the November elections.
Unions and their members made $90 million in donations in the 2000 election cycle, of which 94 percent went to Democrats. Unions made up 11 of the 20 largest political action committee contributors to federal candidates that year.
But Republicans are trying to reach out to skilled-trades unions, which tend to be more conservative politically. Bush also hopes to drive wedges between the Democratic Party and its traditional allies.
"The ground is shifting and the president is proud to have as much labor support as he has," spokesman Ari Fleischer said.
Bush and unions have worked together to push his energy plan, which includes opening Alaska's Arctic National Wildlife Refuge to oil drilling, and imposing new tariffs to help protect the ailing U.S. steel industry.
The carpenters union visited by Bush broke away last year from the AFL-CIO, a major Democratic Party ally. The union, with more than 300,000 members, left because it wanted the labor federation to put more financial emphasis on organizing instead of politics.
Bush, who returned to Washington Sunday after a month at his Texas ranch, will also discuss his legislative agenda and his efforts to bolster America's homeland security after the Sept. 11 attacks, an official said.
He wants to implement the biggest U.S. government reorganization in half a century by folding into a new Department of Homeland Security all or parts of 22 existing agencies, including the Border Patrol, Secret Service and Coast Guard. It would have about 170,000 employees and a budget of around $38 billion.
Bush has already threatened to veto the Democratic-led Senate's version of the bill and will make his case Monday for the House version, which would give him the power to hire, fire and transfer workers in order to ensure efficiency.
The American Federation of Government Employees has denounced the House bill as a union buster and threatened repercussions at the polls.
Bush's Labor Day speech would also include calls for Congress to act on terrorism insurance, pension protections and a comprehensive energy plan, the official said.
On the economy, he said, the president planned to highlight the "bright areas," talking about "how we have low inflation, low interest rates, productivity up."
For the past several months, as the economy has struggled out of recession, Bush has repeatedly assured Americans that the fundamentals of the U.S. economy are sound and that there are signs of strength in the economy.
As a top adviser to his father during the 1992 presidential campaign, Bush saw Democratic challenger Bill Clinton portray the incumbent as insensitive to working Americans while the nation struggled out of recession. Friends and advisers have said the younger Bush has privately vowed to avoid his father's plight.