Can arbitrators in Malta be challenged if I think they’re biased?

Yes, under the Arbitration Act, Chapter 387 of the Laws of Malta, arbitrators are required to disclose any circumstances likely to give rise to justifiable doubts about their impartiality or independence, and a party who becomes aware of such circumstances, including an undisclosed prior relationship with the opposing party, can generally apply to challenge that arbitrator's continued participation in the proceedings, provided the challenge is raised promptly once the relevant facts become known to you, since unreasonable delay in raising a challenge can itself weaken your position. The specific procedure for challenging an arbitrator, including timeframes and the body responsible for deciding the challenge, would be set out in the applicable arbitration rules governing your proceedings, most commonly the Malta Arbitration Centre's rules if your arbitration is being conducted through the Centre, and it's important to follow that specific procedure correctly rather than simply raising informal objections. Given both the seriousness of an undisclosed conflict of interest and the strict procedural requirements around properly raising a challenge, you should consult a lawyer immediately to formally document what you've discovered and pursue the challenge through the correct channel without delay.