No, but some may choose to do so anyway.
In any event, it is important for both parents to check what contractual rights they have to pay while on Shared Parental Leave before making any decisions. If you get full pay for some of your maternity leave, you need to be aware that if you switch to Shared Parental Leave, you could lose out financially.
In an encouraging number of workplaces where unions are recognised, negotiated agreements have been reached on shared parental pay at a level that exceeds the basic statutory minimum, which is just £151.20 per week (from April 2020) or 90% of average weekly earnings if less.
For more information, see the results of the TUC 2016 Equality Audit. For information on how to join a union and on organising union recognition where you work, browse our Union Finder tool.