Learn Portuguese (Portugal): Essa lei é antidemocrática e injusta.

In Portuguese, the prefix anti- attaches directly to the base word. You only use a hyphen if the base word starts with h (like anti-higiénico) or with the same vowel i (like anti-inflamatório). Additionally, if the base word starts with r or s, that letter is doubled instead of using a hyphen (e.g., antissemita). Since democrática starts with d, it simply attaches with no extra changes.

The prefix in- makes injusta the opposite of justa. Does this prefix always stay exactly as in-?

It consistently forms opposites, but its spelling adapts based on the first letter of the root word to make pronunciation smoother. It stays in- before most letters, but changes to im- before p or b (like impossível), ir- before r (like irregular), and il- before l (like ilegal).

Do adjectives with prefixes like anti- and in- still follow normal gender and number agreement?

Yes! Adding a prefix of negation or opposition doesn't change the basic rules of agreement. Because lei is a feminine singular noun, both adjectives must be in their feminine singular forms: antidemocrática (from the masculine antidemocrático) and injusta (from the masculine injusto).