I've don't have any experience with using the words "tithe" or "tithing" where it meant anything other than compulsory donations of 10 percent of your income. Within Mormonism tithing means 10 percent of your income. Every time I had this discussion (mostly door-to-door) with people of assorted Pentecostal churches they always understood it to mean 10 percent. That doesn't mean the term doesn't have flexibility, but I've never it encountered it.
But what would you call it?
That's a fair question and one that I haven't given great thought to, to be honest. It seems like this is more akin to passing around a collection plate. They're becoming more aggressive in putting the issue out in front of the members. They're taking steps to have members establish a set amount of money on a periodic basis.