this is a great question which points to certain nuances in lead link authorities.
The Lead Link, just like any other role, can pitch other roles to take actions and projects. However, it's one thing to pitch because "I think we should do XY”, but another thing to request it from a specific role. Good Lead Link practice would be to first check your role’s definition, and if s/he thinks the needed project fits your role, s/he would request that project from you.
Now, it's up to you as role-filler to interpret your role and decide whether that project requested does sound like a good idea to take on to express your role’s purpose or accountabilities. If you don’t think it does, then the most that the Lead Link can do is try to convince you - but in a way an employee would try to convince her/his boss; the final say remains with the role-filler. If it still doesn’t work, then the Lead Link’s next move could be to go to governance and propose adding accountabilities to your role to include the type of work s/he wants you to be doing in that role. After that modification, s/he can come back to you and request the project again.
Important nuance: Once you’ve agreed to take on a project because you agree it makes sense for your role to take on, - then and only then - the Lead Link has the special authority to prioritize them and ask you to focus on project A before project B. Thus, once you agree to take on a project, the Lead Link authority for prioritizing work becomes relevant and binding for you.
That's my perspective on this. Hope it helps.