A law can not be implemented retroactively.
Exceptionally, only certain provisions of a law can be implemented retroactively, if so required by a general interest determined at the time of the adoption of the law. In that case, the proposer of the law must provide a special explanation of the general interest that requires retroactive implementation of the law.  
In addition, provisions of criminal law can be implemented retroactively only if they benefit the perpetrator of the criminal act.

Choose a quetsion from the Birth of a law

• What is a law?
• Why are laws adopted?
• Which acts regulate the birth of a law?
• Who can propose a law?
• What is a draft law?
• What does a bill look like?
• What are the mandatory elements of the rationale of a bill?
• What are the optional elements of the rationale of a bill?
• To whom is a bill submitted?
• What happens if a bill is not prepared in accordance with the Rules of Procedure?
• When is a bill included in the agenda of National Assmbly session?
• Which National Assembly committees review a bill?
• What is a public hearing?
• What is an amendment?
• Why is an amendment submitted?
• What is a discussion in principle?
• What is a discussion in detail?
• Does the proposer have the right to withdraw a bill from procedure?
• What is the Voting Day?
• How many does the National Assembly make decisions?
• What is urgent procedure?
• What are the specifics of the urgent procedure?
• How is a law promulgated?
• Can the President of the Republic refuse to promulgate a law?
• Who promulgates the law if the President of the Republic neither issues a decree on promulgation nor demands a second vote on the law?
• Is the adopted law published?
• When does a law come into effect?
• Can a law be implemented retroactively?
• Who executes the laws?
• What happens if it is suspected that a law does not comply with the Constitution?
• What happens if the Constitutional Court finds that a law does not comply with the Constitution?
• When does the effect of a law cease?