Answer:
States have a high duty to adhere to the federal laws and state rule as well, wherever it is applicable. But in case the state has unique requirement, it may enact and enforce its own law which suits the local population rather than use of federal law. When it comes to federal drug laws, the states have a responsibility to work along with the federal authorities and government to make sure that the laws are in place. This includes not bringing about conflicting laws.
Congress should allow the employers to set their own rules. For example, if an employer does not allow employees to drink during working hours, there is no problem with it. Similarly if an employer chooses not to hire anyone with visible tattoo on their body, then that is completely employers’ discretion. Similarly if the employers have company wide policy to avoid marijuana, then that is employers’ business. There are many NGOs where the employers do not allow smoking or recruit smokers. There is nothing wrong with it. Now, unless an employee has medical justification for consuming marijuana, the employer should be within their right to decide on action on the employee. This is why Congress should not interfere in the employer-employee relationship.
Given that in absolute conflict, the federal laws trump the state laws, marijuana is not legal in any of the states even if the state law permits it. The only reason the US Government is not taking action against recreational marijuana in the mentioned states is because it is too cumbersome and the outcome is not that significant. There is not a great deal of state benefit by arresting the farmers growing marijuana or the people distributing it. Thus it is still illegal but the government is not acting upon it.