In European parliamentary democracies political parties control candidate selection, maintain cohesion in the legislature and support governments. In addition to these classic functions, parties also organise the legislature delegating power to legislators, specifically as committee chairs and party coordinators. Delegation is inherently dangerous, involving potential agency loss. Parties, however, have ex-ante and ex-post institutional mechanisms to deal with agency problems. In this paper, a case study is made of the Portuguese legislature, arguing that parties make use of their pivotal role in selecting legislators as committee chairs and party coordinators to keep tabs on legislators to thwart shirking from the party line. This paper finds that political parties use incumbency as an ex-ante screening mechanism of committee chairs and party coordinators in looking for reliable signals of past behaviour to decrease uncertainty. Additionally, evidence suggests that extraparliamentary party structure is used as an institutional arena for ex-post control of party coordinators.