Nearly 50,000 dockworkers launched a strike this week at ports from Maine to Texas — but, in a bizarre quirk that has resulted from massive concessions to the union over the decades, the affected ports only employ 25,000.

There’s a massive gulf in the numbers between those who show up for work and total membership in the powerful International Longshoremen’s Association, which won a deal late Thursday for a 62% wage increase over the next six years.

That’s because half of the dockworkers at the East and Gulf coast ports are allowed to sit at home collecting “container royalties” negotiated decades ago to protect against job losses that result from innovation, according to The Wall Street Journal.