In most cases, yes. Before issuing most types of Employment Tribunal claim, including unfair dismissal, discrimination and unlawful deduction from wages, a claimant generally has to notify Acas and obtain an EC certificate first. Without one, the tribunal will usually reject the claim.

There are a small number of exceptions, for example, where another party in the same proceedings has already been through EC, or in certain limited categories set out in the relevant regulations. These exceptions are narrow, so it's not something to assume applies without checking.

Even where EC is required, it doesn't have to result in a settlement. If your employer doesn't want to engage, or you decide not to reach an agreement, Acas will issue a certificate confirming EC has taken place, and you can then proceed to lodge your claim as normal.