The Child Support Guidelines provides a table for the payments that a payor shall make for child support. The payor may make an application for an order to pay child support payments for an amount lower than the guidelines by demonstrating undue hardship.
Section 10(2) of the Child Support Guidelines specify what circumstances could constitute as undue hardship:
(a) the parent or spouse has responsibility for an unusually high level of debts reasonably incurred to support the parents or spouses and their children during cohabitation or to earn a living;
(b) the parent or spouse has unusually high expenses in relation to exercising access to a child;
(c) the parent or spouse has a legal duty under a judgment, order or written separation agreement to support any person;
(d) the spouse has a legal duty to support a child, other than a child of the marriage, who is,
(i) under the age of majority, or
(ii) the age of majority or over but is unable, by reason of illness, disability or other cause, to obtain the necessaries of life;
(e) the parent has a legal duty to support a child, other than the child who is the subject of this application, who is under the age of majority or who is enrolled in a full time course of education;
(f) the parent or spouse has a legal duty to support any person who is unable to obtain the necessaries of life due to an illness or disability. O. Reg. 391/97, s. 10 (2).
http://www.canlii.org/en/on/laws/regu/o-reg-391-97/latest/o-reg-391-97.html