When people enter into an agreement, they do so on the assumption that certain material facts are true, that each is earning as much money as they say they are, that each has no more assets than they say they have, and so forth. These assumptions are the foundation on which the agreement is built. If one of the parties has failed to make full disclosure of these sorts of material facts, or if one party has lied about or misrepresented these facts, the courts may be willing to overturn an agreement.
===Setting aside agreements under the ''Family Relations Act''===
Agreements about property division that were made before March 18, 2013, which is when the ''Family Law Act'' came into force, have to be changed under the ''[http://www.bclaws.ca/civix/document/id/consol21/consol21/00_96128_01 Family Relations Act]'', which was the law in effect before the ''Family Law Act''. If the agreement is between unmarried spouses, then only agreements made before November 24, 2011, would have to be changed under the ''Family Relations Act''.
Section 252(2)(a) of the ''Family Law Act'' says that proceedings to enforce, set aside or replace an agreement about property division that was made before the ''Family Law Act'' came into force must be started under the ''Family Relations Act''. Section 65 of the ''Family Relations Act'' says that an agreement that is in writing and witnessed by a third party or parties can be varied if it would be unfair having regard to the factors set out in that section. Section 68 of the ''Family Relations Act'' provides for the variation of agreements that are not in writing or were not witnessed.
Given the additional issues involved in changing agreements made before March 18, 2013, getting advice from a lawyer is highly recommended.
===Setting aside agreements under the ''Family Law Act''===