To give you number to chew on, each UFT teacher member pays $98.00 a month in dues. Multiply that by 80,000 teachers. There are about 30,000 other titles who pay less, but in the $40-45 a month range. In addition campaigns are run to raise COPE funds specifically for political uses.
I remember COPE, I guess it cuts across all unions. In the IBEW many locals ask you if you want to "contribute" $3.00 /week for COPE. The implication being if you don't then you don't work. Now the amount is nothing, it's just the fact that you're being coerced to contribute to people who's views you oppose. I thought this was something peculiar to the trade unions, I see I was mistaken.