Last year, roughly 25 million Americans used Intuit's best-selling software, TurboTax, to file their federal tax returns, accounting for 35 percent of the company's $4.2 billion in revenue.

With such high profit margins at stake, it comes as no surprise that Intuit would be opposed to free, simple tax returns — already a reality in much of Europe — which could save taxpayers a collective $2 billion and 225 million hours in prep costs and time. The company has spent $11.5 million over the past five years to lobby against return-free filing, claiming that having the IRS as both the collector and preparer of one's taxes is a conflict of interest.

ProPublica's Liz Day sat down with Editor-in-Chief Steve Engelberg to discuss how she came across her investigation; how return-free filing would make tax returns as simple as paying a credit card; and how readers have reacted to her story.

This podcast is available on iTunes and Stitcher. You can also read Liz's investigation, How the Maker of TurboTax Fought Free, Simple Tax Filing, and share how you're filing your taxes this year on our Get Involved page where we'll be charting the results.