Originally founded by Marlin Duval, who led the colonization of the Achenar system in the mid 23rd century, the Empire is based on a 'cliens' system.
Society is strictly stratified, with citizens able to move between strata (lower strata particularly) based on money, patronage and influence.
The Empire values both status and honour very highly indeed. So whilst it is acceptable to flaunt wealth, treating people well is a question of honour, and this duty applies equally to slaves.
Having an unpaid debt is seen as utterly dishonourable. An honourable Imperial citizen would sell themselves into slavery to clear a debt they couldn't otherwise clear.
Law is seen and enforced very differently in the Empire. Senators are responsible for enforcing the Emperor's laws, but the Senators themselves are above the law. They can order executions and can even kill people themselves, though sometimes (rarely) they may be held to account for their actions by the Emperor.
Some Senators are warlike and may take over systems in the name of the Empire to get the spoils, and they may receive a good deal of support from Imperial citizens as a result. Some Senators do not tolerate slavery, and regularly speak out against it, but from the basis of honour. There is little suggestion it should be illegal.
In the Empire, very little is illegal but many things are frowned upon; excessive use of narcotics, in particular.