Should political reporters be barred from political-party membership?

This question has arisen from the controversy around and the inquiry into the political activities of Shane Taurima (as a member of the Labour Party) while working for TVNZ.
An independent report has recommended that any employee of TVNZ with an editorial influence over political reporting should be required not to be a member of any political party and not to carry out any political activity. A regime of mandatory disclosure of party memberships and political activities is recommended for an even wider range of TVNZ staff. No doubt the same principles could be applied to staff at all TV, radio and newspapers.
Is it possible to be a member of a political party and to report political news with impartiality and fairness? I argue that it is possible, provided one is not a highly active member with ambitions for election. Taurima's error was, in my opinion, to mix his political ambitions and activities with his employer's resources, not party membership alone. Taurima was cleared by the inquiry of any bias in his role as a journalist.
Nonetheless, political party membership does compromise the perceived impartiality of a political reporter, and hence it is advisable that reporters not join any party at all.
Conversely, it is equally possible that a reporter may belong to no political party and yet be politically biased or unfair in his or her reporting. Hence, banning party membership alone does not necessarily solve the problem of bias. I just wonder, then, where this could all end up: Should reporters be banned from voting too? Should we bring in the Thought Police to force them to disclose all of their political opinions and expunge them one by one?
OK, that's the reductio ad absurdum. But political party membership and voting are democratic rights in a society like ours. Certainly, at senior levels in journalism (as in the public service) individuals will have to make decisions to distance themselves from political parties and activism, in order to preserve their independence – and to preserve their credibility as employees. But these decisions need to be made individually as a matter of prudent choice. The prospect of an employer (and, in the TVNZ case, a state-owned enterprise) demanding disclosure of employees' party memberships and activities is, in my opinion, an unwelcome and disquieting development. It's a step too far.