It could take away tens of thousands of dollars for some couples over the course of their retirement. 

The rule change goes into effect for new retirees starting in six months. It eliminates a claiming strategy known as "file and suspend." 

Basically, it takes away up to four years of spousal benefits that some people claim before filing for their own benefits. 

This is how it works: At age 66, Joe files for his benefits but immediately suspends them. That means his wife, Jane, can start receiving spousal benefits, equal to half of Joe's full benefit, while Joe's benefit keeps growing for another four years.