I've worked for 2 non-union companies. One that based pay, sick days and holidays on the Teamsters contract even though only about 10% of their employers were union members. The 2nd company observed none of the contract and had their own schedule of holidays. They didn't pay any sick days BUT at the end of the year gave an attendance bonus... small quarterly bonus and doubled if you had all four quarters without missing work. It works great. The only draw back is that you have people coming to work with cold symptoms when you would rather they stay home.
People feel like they have left something on the table if they don't use provided sick day... Alternatively, they feel the same way if they don't collect their bonus because they stayed home with that hangover.
Thats the big issue, how productive is someone who shows up to work with flu? Then ends up infecting another couple coworkers..