What quasi-experimental/econometric technique can I use to measure the impact of a policy using longtitudinal tax data?

I have two cohorts of workers with very similar characteristics (e.g. same demographic profile, skill level, industry) that were laid off at different points in time. Say one group was laid off between 2002-2004 and the other was laid off between 2009-2012.

The first group were laid off with no additional support from their employer. The next group was provided a range of services to help them transition to a new job (call this the treatment group).

I have income tax data, which also includes details such as sex, age marital status etc for the years following these events for much of the two cohorts.

Where would one begin in using this data to attempt to measure the quantitative impact of the treatment (receiving transition support)?

Are there any precedents for such use of tax data? What kind of data analysis or modelling techniques would one use?