It is not stated in Scripture that a person must be baptized before being able to receive the Lord’s Supper. However, the same requirement for both baptism and partaking of the Lord’s Supper is salvation through faith in the death, burial, and resurrection of Jesus Christ.
The Lord’s Supper was instituted by Jesus with His disciples the evening before His crucifixion (Matthew 26:20-28). In Matthew 28:19, after our Lord’s death and resurrection, He gave the Great Commission to His disciples to go into all the world and teach His Gospel, followed with the command to also baptize the new believers. Baptism by water in the name of the Trinity has been practiced by the church from its beginning. The only requirement, as stated above, is that the person has trusted the Lord Jesus Christ as Savior. In doing so, the person understands that this is a picture of the salvation experience and is a requirement of obedience to our Lord. It is considered by many Bible scholars to be the first step of Christian discipleship.
Perhaps this is the reason some churches require baptism before partaking of the Lord’s Supper. The Lord’s Supper is to be partaken of only by believers in Jesus Christ. Baptism is intended to be an identifying mark of believers in Christ. Therefore, some churches require water baptism before a person can partake of the Lord’s Supper. However, again, Scripture nowhere gives us this instruction.