If a freelance agrees a shift or a day job and the client cancels it, the freelance should of course be compensated.
It reasonable for the freelance to charge the full fee for days cancelled with less than a week's notice. However much notice was given, the freelance should receive the full fee if they have turned down other work to fit it in.
As always, our recommendation is to negotiate professionally. You had a contract to do work. If the original work the client had in mind is not there or is not ready on time, is there other work you could do for them?
Several NUJ members have, however, requested a schedule of cancellation charges that they could send to clients. Below we link to a guide, probably most appropriate to shifts on daily papers. You may want to list percentages based on these when confirming commissions, with the statement:
In the event of cancellation of shifts, the following charges apply. Should I find replacement work, there will be no charge.
Text © Mike Holderness & previous contributors; Moral rights asserted. The collection (database right) © National Union of Journalists. Comments to firstname.lastname@example.org please. You may find the glossary helpful.
The National Union of Journalists must not, can not and would not wish to dictate rates or terms of engagement to members or to editors. The information presented here is for guidance and as an aid to equitable negotiation only.
Suggestions apply to contracts governed by UK law only. In any event, nothing here should be construed as legal advice.