Seattle joins Washington, D.C., and San Francisco today as the only government entities to venture where even the federal government and all states except Connecticut have dared not go when its mandated sick leave law takes effect.

In general, workers in Seattle will accumulate one hour of paid sick leave for every 40 hours worked beginning Sept. 1, 2012, provided they work at least 240 hours a year.

The paid sick leave law not only covers personal sickness and leave to take care of family members, but extends its provisions to parents whose children face school or day care closures and to anyone who is the victim of domestic violence.

The law is overseen by the Seattle Office for Civil Rights.

Many businesses are struggling to adopt the new requirements, said Sean Corry, president of Sprague, Israel, Giles, an insurance brokerage firm that works with many nonprofit businesses.

He said one of the complications of the new law is the need to track the hours of employees who spend just part of their work time in Seattle.

"There's a huge amount of compliance required of companies that already have robust sick-leave policies," Corry added.

Michael Chin, in charge of enforcement for the Office for Civil Rights, countered that the goal is "not how many businesses we can find to penalize, but how can we provide assistance to them in implementing this."