"Typically what happens is an employer is aware that the performance of an employee is slipping or inadequate and their level of frustration rises and rises and then it snaps.
"Sometimes it's because the person has been put in the wrong job, or they've been given inadequate training, or expectations are not clear."
Regular performance reviews can help alleviate any workplace blow-ups, Mr Mason said.
Early this month, a Tauranga bus driver had her workplace grievance heard by the ERA after receiving a written warning for refusing to let a child on board because he presented a $20 note to pay his $1.80 fare.
Kay Pridmore was issued the warning last October by Go Bus Transport after leaving the child behind and then later telling her supervisor if she wanted to give change she would work in a "f***ing bank".
Ms Pridmore took Go Bus to the ERA because she said the warning she received about her behaviour unjustifiably disadvantaged her employment. The authority found she had not been unjustifiably disadvantaged.
Earlier this month, a Nelson rest home worker dismissed after hiding behind a door when discovered with a gardener in a dead resident's flat was awarded more than $10,000 for legal costs when she took her case to the ERA - on top of more than $6275 already awarded for lost wages and compensation.
However, an Oamaru meat worker sacked for squirting a colleague in the face with a high-pressure hot water hose failed to get his job back following an ERA decision.
In the past two years, 811 of the authority's determinations ruled in favour of the employee and 691 in favour of the employer.
Employers and Manufacturers Association employment services manager David Lowe said despite the ratio of determinations favouring workers, he did not believe the authority was biased.
"I think that the employment law requirements that it is their job to interpret are difficult for employers to get right.
"We certainly know from the statistics that when it comes to performance-related matters, employers get that wrong 85 per cent of the time."
The authority had been working hard to improve consistency between authority members' determinations, Mr Lowe said.
"Previously the Wellington authority was operating quite differently to the rest of the country ... The average awards were much higher than anywhere else."
The average cost to an employer when they lost a grievance was $35,000, which was "almost crippling for some small businesses", he said.
Last year the ERA received 1985 hearing applications; however only 914 cases made it through the full ERA hearing process. Most were settled by mediation.
The authority was established in 2000. Cases are heard in Auckland, Wellington and Christchurch and determinations are legally binding.
Parties unhappy with an ERA decision can appeal to the Employment Court.
By the numbers
55 Tauranga and Western Bay of Plenty ERA applications received in 2012, 20 determinations.
35 Tauranga and Western Bay of Plenty ERA applications received in 2011, 25 determinations.
1985 total ERA applications received nationwide in 2012, 914 determinations.
397 found in favour of employee, 311 in favour of employer.
2239 total ERA applications received nationwide in 2011, 958 determinations.
414 found in favour of employee, 380 in favour of employer.
