What is the purpose of Schedule C in Form 990-EZ?

Schedule C is attached by an organization along with the IRS Form 990-EZ, if the organization participated or intervened in (including the publishing of statements) any political campaign or lobbying activities on behalf of (or in opposition to) any candidate for public office, either directly or indirectly. 
 
In addition to it, every section 501(c)(3) organization that had a section 501(h) election in effect during the tax year must complete Schedule C Part II-A, regardless of whether they engaged in lobbying activities during the tax year or not.