“Masters, … Do not threaten (your slaves)”. 

Eph 6:9 NIV 
The relationship between employer and employee is fraught with a number of problems. One of these is the nature of the relative power wielded by each. This is affected by the age of the two, a young employee being in a weaker situation than a senior person who is the boss. It may be affected by the gender as well, and male employers quite often take advantage of female employees. The competence and qualification of the employee will affect things as well. A person with high and scarce qualifications can wield more power than the employer might like. 
With sixty million slaves in the Roman Empire, the master was in a strong position. Any trouble or difficulty from a slave and he could go and get another one. There were no complicated labour regulations protecting workers in those days. In fact there was nothing protecting them. The owner made his own labour laws as he went along. This meant the slave was in a very weak position indeed and physical violence was often used by the more aggressive masters. Paul knew this and hence demanded that the Christian master restrain himself from resorting to violence or threats (that is clearly the hint behind the mention of threats) in order to get the slave to obey his orders. It obviously had been a problem, otherwise Paul would not have thought of mentioning it. 
There are some work situations today where employers feel they need to put pressure on their workers to get production up and to meet targets. Christian people in these positions need to remember this warning from the apostle Paul and to act with dignity, tact and understanding. 

PRAYER THOUGHT Lord, make me a responsible and caring employer.