Paid political advertising or underwriting messages from poltical campaigns are prohibited under the Communications Act. If they want free airtime on the station, then that's up to the station.
You are required to track all requests received by polticial candidates for airtime in your poltical file, even if you turn down their request. Political file data must be retained for at least two years. Your political file is a part of your station record and must be presented if requested during an inspection. LPFM (and other non commercial stations) are prohibited from endorsing poltical candidates per section 399 of the Communications Act. Endorsements may also violate state and IRS regulations. REC's advice is for LPFMs to always steer clear of politics.