Revenue raising options, including PRSI, are considered in the context of Budget preparations. However, I would point out that taxes on employment are generally considered more damaging economically than other taxes such as capital taxes, as they increase the costs to employers of creating additional jobs.
Costings in relation to PRSI increases are prepared by the Department of Social Protection. In addition, that Department prepares an annual paper on Pay Related Social Insurance for discussion at the Tax Strategy Group, which meets in advance of the Budget. All of the tax strategy group papers are published on my Department's website annually. The 2014 paper on PRSI is available at the following link: http://www.finance.gov.ie/sites/default/files/14.08%20Pay%20Related%20Social%20Insurance.pdf.