What action involves groups of people trying to influence policy decisions?

The action that involves groups of people trying to influence policy decisions is lobbying. This process typically includes organized groups, such as interest groups or advocacy organizations, that engage with lawmakers and government officials to advocate for specific legislation or policy changes. Lobbying is an essential part of the political process as it allows various stakeholders, including businesses, non-profit organizations, and community groups, to present their views and push for policy outcomes that align with their interests and goals.

In contrast, monitoring usually refers to the systematic observation of processes or policies to assess their implementation and effectiveness. Advising entails providing recommendations or guidance based on expertise but does not inherently involve attempts to change policy. Collaborating involves working together towards a common goal, which can include influencing policy but is more about teamwork and partnership than direct advocacy. Therefore, lobbying specifically focuses on the effort to influence policy decisions directly, making it the correct choice.