President Obama Monday proposed a $50 billion plan to rebuild America’s roads, rails and runways, calling it an investment that will move the country’s economy forward and leave the next generation something lasting.

Obama’s Labor Day speech to a union crowd mixed his proposal to invest in the country’s infrastructure with an ode to the middle class and a series of swipes at Republicans. The president told the union crowd “you’re the reason I’m here” as he promised to fight for the country’s middle class.

His infrastructure proposal builds on the economic stimulus package the administration pushed through last year and includes a six-year plan to rebuild 150,000 miles of roads, construct and maintain 4,000 miles of rail, and rehabilitate and construct 150 miles of runways. It also calls for a next generation air-traffic control system to reduce travel time and delays.