Final answer:
The Municipal Securities Rulemaking Board (MSRB) enforces the rules designed to prevent 'pay to play' activities in the municipal securities market.
Step-by-step explanation:
The rules to prevent pay to play regarding contributions made to political parties, candidates, and elected officials by firms involved in the underwriting or sales of municipal securities are enforced by the Municipal Securities Rulemaking Board (MSRB). This independent regulatory organization was established to protect investors and the public interest by promoting a fair and efficient municipal securities market and ensuring that municipal entities have access to high-quality professional services. It works alongside other regulatory entities such as the Securities and Exchange Commission (SEC) and the Financial Industry Regulatory Authority (FINRA) to oversee the municipal securities industry.