American retail workers have now lost jobs for the fourth straight month, locking in a trend in which shoppers are spurning bricks-and-mortar shops and buying on-line.

The U.S. economy added 138,000 new jobs in May, and the unemployment rate dipped to 4.3%, according to a report issued Friday by the Labor Department. Markets won't be too disappointed with these headline numbers, even though job growth was below economist expectations by roughly 50,000.

Data: Bureau of Labor Statistics; Chart: Lazaro Gamio / Axios

But retail had another tough month: In retail, 6,100 people lost their jobs, adding up to 80,300 since the start of the year, the government said. This falls in line with the US and global shift to on-line shopping.

A level deeper: The trend occurs in one of the country's primary job sectors: some 15.9 million US workers are employed in retail, which has been a vital entry point for low-skilled workers, and a safe harbor for those who have fallen out of other jobs.

Be smart: If this trend continues, the U.S. worker may lose a vital step on the ladder of economic mobility. Workers often earn only minimum wage, but without bricks-and-mortar stores and malls, it's hard to see where those employed in them will find other work.