Yes Equifax has accumulated employment and income information through their purchase of The Work Number (https://en.wikipedia.org/wiki/The_Work_Number) in 2007. They have 200 million of employment records and likely a higher multiple of paychecks.
They have a large share of the fortune 500 companies in the US. If you have worked for a large firm in the past, it's likely that every single one of your paycheck is somewhere in their database.
