Your lease must provide you with the right to late fees. Even if it does, you may have waived yoru right by continually accepting rent without charging late fees. Otheriwse, it's enforceable with a 7-day notice to tenant.
Typically these terms would need to be in the lease but you do need to be careful as to whether you have waived any rights to collect. I would suggest speaking with an attorney and letting them review your lease.
The above is general legal and business analysis. It is not "legal advise" but analysis, and different lawyers may... moreThe above is general legal and business analysis. It is not "legal advise" but analysis, and different lawyers may analyse this matter differently, especially if there are additional facts not reflected in the question. I am not your attorney until retained by a written retainer agreement signed by both of us. I am only licensed in California. See also avvo.com terms and conditions item 9, incorporated as if it was reprinted here. Please visit my web site: www.avanesianlaw.com for more information about my services. less