From the article:
The group was formed in 2000 with money from the American Federation of State, County and Municipal Employees. It has four employees, led by Mr. Lux. It has Section 501(c)4 tax status, which means it cannot run advertisements mentioning specific candidates within 60 days of a general election or 30 days of a primary. The status also lets the group keep the identities of its backers a secret.