Our 501(c)(3) educational organization operates solely on membership contributions. One of our primary activities is to work one on one training local governments on the laws which allow them to coordinate local plans and policies with those of state and federal agencies. This includes traveling to their locations and spending several days. Local governments are reluctant to make contributions to us for fear of showing favoritism, so we often recoup only travel costs. May we charge a fee for these services?
Yes. Charities charge fees for all sorts of services and so long as the work is within the educational purpose for which you are exempt, the fees will not create unrelated business taxable income. You may face a whole new set of issues with governmental procurement laws, but if you retain your flexibility and tailor your arrangement to achieve what works, you should be able to increase your income.
You may be thinking of the limit on the amount of earned income that qualifies as public support for an organization that seeks to qualify under Section 509(a)(2) of the Tax Code. The amount of any payment that can be counted as public support in each year is 1% of total support from the year. With a broad range of fee payers and contributors, that should not be a problem. And if the organization is primarily funded through contributions so that it qualifies as publicly supported under 509(a)(1) and 170(b)(1)(A)(vii) instead of 501(a)(2), it will not be an issue at all.