More American employees may voluntarily quit their jobs this year as increases in wages and openings boost confidence in the labor market, Bloomberg reported.

About 2.2 million U.S. workers resigned in December, a 7.4 percent increase from a year earlier, based on seasonally adjusted data from the U.S. Department of Labor. Those employees represent 53 percent of total separations, the highest number since 2008.

That ratio was 37 percent in April 2009, the lowest since the data began to be collected, according to Nicholas Colas, chief market strategist at ConvergEx Group, an institutional equity-trading broker in New York.

Readings above 50 percent imply an improving economy.

The share of Americans who say business conditions are "good" minus the share who say they are "bad" fell to minus 10.7 percentage points in January, down from minus 9.1 points the prior month, which was the strongest level in more than four years, according to the research group known as The Conference Board.