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Yes, it's ONLY for rent.
2015 ORS 90.260¹
(1) A landlord may impose a late charge or fee, however designated, only if:
(a) The rent payment is not received by the fourth day of the weekly or monthly rental period for which rent is payable; and
(b) There exists a written rental agreement that specifies:
(A) The tenant’s obligation to pay a late charge on delinquent rent payments;
(B) The type and amount of the late charge, as described in subsection (2) of this section; and
(C) The date on which rent payments are due and the date or day on which late charges become due.
(2) The amount of any late charge may not exceed:
(a) A reasonable flat amount, charged once per rental period. "Reasonable amount" means the customary amount charged by landlords for that rental market;
(b) A reasonable amount, charged on a per-day basis, beginning on the fifth day of the rental period for which rent is delinquent. This daily charge may accrue every day thereafter until the rent, not including any late charge, is paid in full, through that rental period only. The per-day charge may not exceed six percent of the amount described in paragraph (a) of this subsection; or
(c) Five percent of the periodic rent payment amount, charged once for each succeeding five-day period, or portion thereof, for which the rent payment is delinquent, beginning on the fifth day of that rental period and continuing and accumulating until that rent payment, not including any late charge, is paid in full, through that rental period only.
(3) In periodic tenancies, a landlord may change the type or amount of late charge by giving 30 days’ written notice to the tenant.
(4) A landlord may not deduct a previously imposed late charge from a current or subsequent rental period rent payment, thereby making that rent payment delinquent for imposition of a new or additional late charge or for termination of the tenancy for nonpayment under ORS 90.394 (Termination of rental agreement for failure to pay rent).
(5) A landlord may charge simple interest on an unpaid late charge at the rate allowed for judgments pursuant to ORS 82.010 (Legal rate of interest) (2) and accruing from the date the late charge is imposed.
(6) Nonpayment of a late charge alone is not grounds for termination of a rental agreement for nonpayment of rent under ORS 90.394 (Termination of rental agreement for failure to pay rent), but is grounds for termination of a rental agreement for cause under ORS 90.392 (Termination of rental agreement by landlord for cause) or 90.630 (Termination by landlord) (1). A landlord may note the imposition of a late charge on a nonpayment of rent termination notice under ORS 90.394 (Termination of rental agreement for failure to pay rent), so long as the notice states or otherwise makes clear that the tenant may cure the nonpayment notice by paying only the delinquent rent, not including any late charge, within the allotted time.
(7) A late charge includes an increase or decrease in the regularly charged periodic rent payment imposed because a tenant does or does not pay that rent by a certain date. [1989 c.506 §15; 1995 c.559 §8; 1997 c.249 §30; 1997 c.577 §9a; 1999 c.603 §12; 2005 c.391 §16; 2007 c.906 §32a]
The for cause and termination by landlord require 30 days notices (https://www.oregonlaws.org/ors/90.392, https://www.oregonlaws.org/ors/90.630). So if it's more than rent, if the rent is paid but not the extra charges, a 30 day notice would have to be used.
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