In recent years, web-push strategies have been developed in cross-sectional mixed-mode surveys to improve response rates and reduce the costs of data collection. However, pushing respondents into the more cost-efficient web mode has rarely been examined in the context of panel surveys. This study evaluates how a web-push intervention affects the willingness of panel members to switch survey modes from mail to web. We tested three web-push strategies in a German probability-based mixed-mode panel by randomly assigning 1,895 panelists of the mail mode to one of three conditions: (1) the web option was offered to panelists concurrently with the paper questionnaire including a promised €10 incentive for completing the survey on the web, (2) the web option was presented sequentially two weeks before sending the paper questionnaire and respondents were also promised an incentive of €10, or (3) same sequential web-first approach as for condition 2, but with a prepaid €10 incentive instead of a promised incentive. The study found that a sequential presentation of the web option significantly increases the web response in a single survey but may not motivate more panelists to switch to the web mode permanently. Contrary to our expectation, offering prepaid incentives neither improves the web response nor the proportion of mode switchers. Overall, all three web-push strategies show the potential to effectively reduce survey costs without causing differences in panel attrition after five consecutive waves. Condition 2, the sequential web-first design combined with a promised incentive was most effective in pushing respondents to switch to the web mode and in reducing costs.