Political party is a personal choice and thus not a protected class.
Freedom of association permits us to choose who we do and do not associate with based on that individual's own choices.
Freedom of association permits us to choose who we do and do not associate with based on that individual's own choices.
There are laws in place to prevent employers from coercing employees into political action - i.e. you won't get your annual bonus unless you donate to this political candidate - but these are protections from extortion, and not exceptions to the general rule that political party is not a protected class.
When it comes to discrimination of employees by employers, then the protected classes, personal choice, and freedom of association are highly relevant irrespective of country.