In general, according to the IRS, "no organization may qualify for section 501(c)(3) status if a substantial part of its activities is attempting to influence legislation (commonly known as lobbying). A 501(c)(3) organization may engage in some lobbying, but too much lobbying activity risks loss of tax-exempt status."
Whether a 501(c)(3) nonprofit's activities constitute a "substantial part" of their overall activities is ultimately up to the IRS to decide on a case-by-case basis. The IRS makes its determination based upon the amount of time spent (by both volunteers and staff), as well as the amount of money expended for such activities. Organizations that fail to meet the substantial part test and/or the expenditure test are at risk of losing their tax-exempt status and may be subject to excise taxes.
Keep in mind that 501(c)(3) nonprofits are strictly prohibited by the IRS from participating in campaigns for (or against) political candidates to public office. The IRS page on political activities explains this rule more thoroughly.
You will need to seek counsel from a legal consultant in the event that your organization has specific legal questions pertaining to these federal rules. For more information on locating legal help for your nonprofit, please see our Knowledge Base article, Where can I find technical assistance or a consultant for my nonprofit?
Lobbying Guidelines for Public Charities
Independent Sector
The resources on this page explain what is considered lobbying, how much lobbying a 501(c)(3) organization can do, and whether an organization that does federal lobbying needs to register with Congress and follow Congressional gift rules.
NEO Law Group provides corporate, tax, and charitable trust law counsel to nonprofit and tax-exempt organizations, as well as board trainings and group presentations to address specific issues of importance to nonprofit clients.
Introduction to Lobbying by Public Charities
Nonprofit Law Blog
General Rule: No substantial part of the activities of an organization described by IRC Section 501(c)(3) may be the carrying on of propaganda or otherwise attempting to influence legislation.
527s: Advocacy Group Spending (web database)
OpenSecrets
Shows the major players who give and receive money from 527 organizations.
Non-Profits CAN Lobby
Center for Non-Profits
Knowing what constitutes lobbying under the law, and what the limits are, is the key to being able to lobby legally and safely. This article represents a vastly simplified summary of some of the laws and regulations governing charitable lobbying.
Everyday Advocacy
National Council of Nonprofits
Advocacy doesn't have to be complicated. This featured section demonstrates how effective it can be in advancing your nonprofit's mission.
Lobbying
IRS
In general, no organization may qualify for section 501(c)(3) status if a substantial part of its activities is attempting to influence legislation (commonly known as lobbying). A 501(c)(3) organization may engage in some lobbying, but too much lobbying activity risks loss of tax-exempt status.
Measuring Lobbying: Substantial Part Test
IRS
Whether an organization's attempts to influence legislation, i.e., lobbying, constitute a substantial part of its overall activities is determined on the basis of all the pertinent facts and circumstances in each case. Under the substantial part test, an organization that conducts excessive lobbying in any taxable year may lose its tax-exempt status, resulting in all of its income being subject to tax.
Stand for Your Mission
BoardSource
The Stand for Your Mission campaign promotes the importance of organizational advocacy, providing board members with the tools to attract and retain ambassadors for their organization.
The Restriction of Political Campaign Intervention by Section 501(c)(3) Tax-Exempt Organizations
IRS
Under the Internal Revenue Code, all section 501(c)(3) organizations are absolutely prohibited from directly or indirectly participating in, or intervening in, any political campaign on behalf of (or in opposition to) any candidate running for office.