What's Going On With the Unions?

I've read in the Times and the Washington Post about this big split where the Teamsters, the Service Employees International Union and several other large unions are leaving the AFL/CIO. But I can't tell from these articles what it's all about. The only thing they mention is dissatisfaction with loss of membership, but there's no indication of what specifically the dissidents object to or would do differently. It seems rather obvious that the biggest problem for unions is the high rate of immigration. Unions in America reached their peak power during the highly restrictive immigration period of 1925 thru 1965. But then labor's biggest champion, Teddy Kennedy, set organized labor on its unabated road to ruin with his open borders immigration act of 1965. I'm hoping that maybe immigration is the secret reason for the split but no one wants to come out and say it.