"Assuming that the trend towards mobile continues and your mobile monetization efforts are unsuccessful, ensure that your disclosure fully addresses the potential consequences to your revenue and financial results rather than just stating that they 'may be negatively affected,'" the SEC wrote in a Feb. 28 letter to Facebook Chief Financial Officer David Ebersman.

In another letter to Ebersman dated March 22, the SEC asked whether Facebook's mobile monthly average users, or MAUs, were increasing in regions where the use of PCs was less prevalent.

Facebook responded by changing some of its disclosures in amended IPO filings.

In a March 27 letter to the SEC from Facebook's lawyers at Fenwick & West, the company said it updated disclosures to include information on countries where it experienced the most significant growth in mobile MAUs.

However, Facebook also noted that it had seen growth in mobile MAUs in countries where PC use was prevalent, such as the United States, as well as countries where PCs are not so popular, such as Mexico.

This back and forth between the SEC and companies is typical during big IPOs.

"We responded to all SEC comments over the course of this correspondence and the SEC declared our registration statement effective on May 17," a Facebook spokesman said on Friday.

However, the growth of mobile Facebook users became a big issue toward the end of the IPO process. On May 9, the company updated its IPO filing to warn that advertising growth was not keeping up with user growth in the second quarter, as more people accessed the social network through mobile devices.

That additional disclosure was not in response to SEC questions. Instead, Facebook had seen a continuation of the mobile trend during the first month or so of the second quarter and decided to update investors.

The amended May 9 IPO filing triggered estimate cuts by analysts at the banks underwriting the IPO, putting a financial and legal cloud over the offering.