Federal legislation is enacted by the Federal Assembly, i.e. the Parliament (legislature).
Any person or body that wants a new law to be enacted or an existing law to be changed, whether they are citizens (i.e. with the right to vote at federal level), interest groups, members of parliament, cantons or the Federal Council, can submit their request to the federal parliament.
However, it is parliament that ultimately decides whether a law should be amended and how it should be amended.