A long-awaited liftoff in the U.S. economy is facing pressure from stubbornly weak wage growth, muddying the outlook for consumers and challenging Federal Reserve policy makers who are counting on a pickup as they unwind the central bank's extraordinary support for the recovery.

Growth in wage and salary income slowed to just 0.2% in April from the prior month, marking the weakest monthly increase of the year, the Commerce Department said Friday. After adjusting for inflation, wage and salary income was up 2% from a year earlier. The figures came in a report showing that U.S. consumer spending fell in April for the first time in a year even while inflation crept up.

The weak start to the second quarter, coming after the U.S. economy in the first quarter contracted for the first time in three years, is challenging the thesis of economists and investors who have been counting on a 2014 growth breakout. Those expectations have pushed U.S. stock benchmarks to record levels, while yields on safe Treasury bonds have dipped in part due to softer economic data.

The S&P 500 index hit a fresh record Friday, rising 3.54 points, or 0.2%, to 1923.57. It advanced 2.1% in May. Bonds also rallied during May, with the 10-year Treasury note posting its biggest monthly drop in yield—which moves in the opposite direction of its price—since January. Muted selling Friday pushed the yield up slightly to 2.459%.

"We are not seeing job gains translate into wage pressures," said Sterne Agee chief economist Lindsey Piegza. "It's a question not just of quantity but also of quality" of the new jobs being created, with many temporary or part-time jobs coming in low-paying industries, she said.