Rules vary by location. This article focuses on Great Britain, with the distinctions for Ireland and Northern Ireland covered below. Moving a shift can look like a straightforward staffing decision, but employers generally can’t change contractual working hours without agreement. A valid flexibility clause may allow a change if you use it reasonably.
For your business, the risk starts when an updated rota changes contractual working hours without agreement. Start with the contract, then settle the process.
Key takeaways
Consultation doesn’t replace consent. A business reason alone doesn’t permit changing agreed contractual terms. Flexibility clauses have limits, notice doesn’t cure a breach, and an employee’s silence isn’t reliable evidence of agreement.
When can you change contractual working hours?
Read the clause before changing the rota
Check the agreed hours, shift pattern and any flexibility clause in your contract. These are contractual terms, so the contract protects the hours and pattern you’ve agreed. Our guide to UK employment contract terms explains what those documents should cover.
A tribunal may read a variation clause narrowly. A clause allowing changes to shift times may not cover reductions to guaranteed hours or pay.
Acas’s flexibility clause guidance explains that clauses can have specific boundaries. Consult affected employees, give reasonable notice and consider childcare, disability and travel difficulties.
Calculate the effect beyond the rota
Reducing 40 hours to 32 at an unchanged hourly rate cuts gross pay by 20%. Pension contributions and holiday pay may also change. Account for leave already accrued.
Extra hours must have a contractual basis or be agreed. Under the Working Time Regulations 1998, most adult workers face a 48-hour average weekly limit unless they’ve voluntarily opted out. Rest requirements still apply.
Consultation, agreement and notice
Explain the proposal and record agreement
Set out why the change is needed, who it affects and what happens to pay and benefits. Give employees time to respond and consider alternatives, including phased implementation or different shifts.
HR, operations and finance should work from the same proposal. Otherwise, payroll may implement something the employee never accepted.
Check any applicable collective agreement and whether a recognised trade union must be involved or has relevant terms.
Record agreement and the start date. Changes to required written particulars must normally be confirmed in a written statement within one month. Written confirmation doesn’t itself prove agreement or consent.
Separate change notice from dismissal notice
There’s no universal statutory notice period for an agreed hours change. Follow applicable contractual requirements and agree the start date.
If you’re ending the existing contract, statutory dismissal notice normally means one week after one month’s service, until two years. It then increases to one week per completed year, capped at 12 weeks.
After three completed years, that’s three weeks. If the contract promises one month, give the longer period.
If roles are genuinely being reduced, consider whether redundancy requirements apply. Treat that separately from a change to contractual hours.
Giving dismissal-length notice doesn’t, by itself, authorise you to impose new contractual hours.
What happens if an employee refuses?
Keep discussing alternatives rather than treating refusal as misconduct. Unilateral imposition of changes can lead to unlawful deduction, breach of contract or constructive dismissal claims.
Employees who object should write promptly, explain if they’re working under protest and raise a grievance. They should get legal advice before resigning. Silence or continuing to work doesn’t necessarily amount to implied consent, so don’t rely on it.
Fire and rehire remains a high-risk option. The Code of Practice on Dismissal and Re-engagement, effective since 18 July 2024, requires meaningful consultation and treats dismissal as a last resort. Employers should contact Acas before raising that possibility with staff.
As at October 2026, the Employment Rights Act 2025’s new fire-and-rehire restrictions aren’t yet in force. The forthcoming rules make dismissal for refusing restricted changes, including hours and pay, automatically unfair, subject to a narrow exception involving serious financial difficulties.
Ordinary unfair dismissal generally still requires two years’ service in October 2026. Discrimination and many automatically unfair dismissal claims don’t.
Proposing dismissal and re-engagement for 20 or more employees at one establishment within 90 days triggers collective consultation duties. Affected employees may bring relevant claims before an employment tribunal. TUPE also restricts transfer-related changes, even where employees agree.
Get specialist advice before either process starts.
How Ireland’s rules differ
This guidance primarily covers Great Britain. Northern Ireland has separate employment legislation.
In Ireland, Citizens Information’s contract guidance distinguishes contractual terms from non-contractual work practices, such as rostering and breaks. Changes to contractual terms generally need agreement.
Written details must be provided by the effective date, or before departure for overseas work. Workplace Relations Commission complaints normally have a six-month deadline, which can be extended by six months for reasonable cause.
Frequently asked questions
Does a zero hours contract allow any shift change?
Genuine zero hours contract arrangements generally don’t guarantee work, but the label alone doesn’t determine contractual rights. Review agreed terms and established working patterns before withdrawing regular shifts. Minimum wage, holiday and discrimination protections still apply.
Can employees be required to work extra hours?
A lawful overtime clause may require additional hours within its terms. Without that basis, seek agreement. Extra work must still respect working-time limits, rest requirements and minimum wage rules.
Agree the change before implementing it
The safest process keeps the contract, consultation record and payroll instructions consistent. Deal with objections before the new rota goes live.
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Book an intro call to discuss support before changing your team’s contractual hours.