The Office of Government Ethics has issued a legal advisory reminding executive branch employees that ethics laws and regulations continue to apply during the time that they are in a furlough status.
The advisory, LA-13-02, referrs to to guidance first issued in 2004 that applies to those in furlough status, available at: http://www.oge.gov/DisplayTemplates/ModelSub.aspx?id=1388
It also cited OPM guidance available here:
OGE called on agency ethics officials to remind employees they must continue to comply with all of the ethics laws and regulations, including criminal conflict of interest laws, the Standards of Ethical Conduct for Employees of the Executive Branch, and any agency-specific supplemental standards of ethical conduct, particularly provisions on outside activities, while they are in a furlough status.