WASHINGTON (AP) — The federal agency that insures pensions for about 41 million Americans saw its deficit nearly double last year. The agency said the worsening finances of some multi-employer pension plans mainly caused the increased deficit.

At about $62 billion for the budget year that ended Sept. 30, it was the widest deficit in the 40-year history of the Pension Benefit Guaranty Corp., which reported the data Monday. That compares with a $36 billion shortfall in the previous year.

Multi-employer plans are pension agreements between labor unions and a group of companies, usually in the same industry. The agency said the deficit in its multi-employer insurance program jumped to $42.4 billion from $8.3 billion in 2013.

By contrast, the deficit in the single-employer program shrank to $19.3 billion from $27.4 billion.