Reasons to contact an employment lawyer:

1. You want to understand your contractual rights!
You are not being paid your bonus or another benefit in your contract has been breached. (FAQS: Wrongful dismissal, Restrictive covenants, moving as a team, Bonus and commission claims).

2. You want to know your statutory rights!
The most usual are unfair dismissal rights, simply - to be treated fairly if your employment is to be terminated. (FAQS: Compensation, Negotiating Severance agreements, Compromise Agreements, Unfair dismissal, Constructive dismissal, Redundancy, My employer has started a disciplinary hearing). 
The main ways to dismiss an employee is that their conduct or performance is unsatisfactory. (FAQS: Unfair dismissal, My employer has started a disciplinary hearing).

Or, perhaps there is no use for them anymore and that they should be made redundant. (FAQS: Redundancy, Compromise agreements, Negotiating Severance agreements).

Perhaps the employee is experiencing discrimination or harassment. (FAQS: Discrimination).        

3. Compensation:There are many situations where an employee may claim unfair dismissal, wrongful dismissal, constructive dismissal or some combination of these. Sometimes it is clear and apparent or it may be disguised as a redundancy situation and you will need advice from an employment lawyer to determine if you have a claim and how good your employment law claim is. Whatever the case, if you have claim, one of the first priorities is how to meet your mortgage payments and other bills and a crucial issue will be how much money you can get if you bring an employment law claim.

4. Unfair Dismissal: This depends on the type of employment law claim you bring. In unfair dismissal (which can include constructive dismissal) the maximum compensation payable by the Tribunal is in excess of £60,000. There is NO limit to the maximum amount of compensation if the claim is for discrimination. For wrongful dismissal the damages are what you would have been entitled to under your employment contract, if you had not been wrongfully dismissed. A wrongful dismissal claim is often why you hear of football managers who are sacked being ‘paid out their contract'. contrary to popular belief, very little is awarded for ‘hurt feelings' - typical awards are from a few hundred pounds to a few thousand pounds. In all cases, there is what is known as a ‘duty to mitigate your loss'. This simply means you are expected to try to find another job. If it takes you 2-3 months to find another job, then you would be entitled to compensation equivalent to the amount you would have been paid under your contract for that time. In terms of salary and other benefits all this is relatively straightforward to calculate. However, if you are also entitled to a bonus it can become much more complex and specialized employment law advice would probably be beneficial.

5. Unfair Dismissal
Not all compensation is the result of an unfair dismissal claim. You may have an employment law claim for a bonus without a dismissal. If you do have an unfair dismissal claim or a wrongful dismissal claim then your bonus or commission payment may be a vital part of the compensation you are seeking.
Bonus schemes are popular with employers. A bonus system can be effective in motivating employees and a useful tool in rewarding and retaining top performing employees. However, they are also a rich source of employment law disputes, both in unfair dismissal, wrongful dismissal, discrimination and contract claims.
For quite some time, many employers have looked to make bonuses discretionary - a bonus system is used to motivate and reward employees but one that is entirely at the employer's discretion. Where an employer has a bonus scheme with open rules, or entitlement to a bonus is set out in the contract, it is easy for the Court to include the bonus in any award made to the employee, provided that the employee would have been employed at the time the bonus vested, if he or she had not been wrongfully dismissed.
The more difficult question has always been where the bonus is expressly stated to be discretionary and there are no fixed rules as to how it is determined. Unsurprisingly, this dilemma has produced a flood of case law. Effectively the Courts have now concluded that a discretionary bonus can only be determined at the employer's discretion to the extent that the employer's decision is bona fide and rational. This is the case even if the decision whether to pay a bonus at all is discretionary. If the employer decides not to pay that ‘discretionary' bonus and that decision is not rational or bona fide then the Court must make its own rational judgment as to whether the employee would have been paid and a bonus and how much that bonus would have been.