UPDATE 1-Le Pen as president would seek French electoral law change -aide
(Adds background on constitutional rules)
PARIS May 3 Presidential candidate Marine Le Pen would try to change France's electoral law by referendum if she wins the presidency on Sunday and her National Front (FN) party fails to win a parliamentary majority in June, a senior FN official said.
Le Pen, who is standing against centrist candidate Emmanuel Macron in Sunday's presidential run-off, would then call new elections under the new rules.
France holds parliamentary elections on June 11 and 18.
"If the new Assembly is hostile to us, we would change the electoral law via a referendum organised as soon as next summer, then the president would dissolve the National Assembly," Gilles Lebreton, the FN official told Le Canard Enchaine newspaper.
Le Pen's official manifesto states that she would implement proportional representation with a 30-percent bonus for the party which came first in the election.
France's existing two-round voting system has so far ensured that despite winning about a quarter of the votes in recent elections, the FN has only two members of parliament.
In the 2014 European parliamentary election, the FN came first in France with 24.84 percent of the vote.
Unlike presidential election rules, parliamentary election rules do not require a constitutional change. The president can invoke article 11 of the constitution to call a referendum and amend laws on "the organisation of political powers" after a request by the government.
Opinion polls show Macron defeating Le Pen on Sunday 60-40. (Reporting by Michel Rose; Editing by Louise Ireland)