Patricia Arquette injected some political fervour into the Oscars ceremony by calling for equal pay for women at the end of her acceptance speech for best supporting actress.

Arquette had been widely expected to win the award for her role in Boyhood, in which she plays Olivia, the mother of Mason, in a performance filmed over 12 years.

However, her speech was much more surprising. It began conventionally enough, with Arquette paying tribute to her cast members, family, and boyfriend Eric White, “my favourite artist in the world”.

It concluded with the impassioned words: “To every woman who gave birth, to every taxpayer and citizen of this nation, we have fought for everybody else’s equal rights. It’s time to have wage equality once and for all. And equal rights for women in the United States of America.”

Her speech received wild cheers from the audience, with Meryl Streep and Jennifer Lopez getting out of their seats and waving their arms.

just this for the rest of my life #PatriciaArquette pic.twitter.com/t2D765Km8i — Julie Murphy (@andimJULIE) February 23, 2015

Equal pay is as controversial a subject in Hollywood as in the rest of America. The hacked Sony emails had revealed wide disparity between the pay of men and women in Hollywood. On American Hustle, the male stars were paid 9% of the profits, while Amy Adams and Jennifer Lawrence were on 7% each – despite the fact that Lawrence was an Oscar-winner at the time.

Backstage clutching her Oscar, Arquette repeated her call for equality in Hollywood. “It is time for us. Equal means equal.”

It was inexcusable that celebrities travelled the world preaching equal rights when at home “under the surface” women, gays and people of colour struggled to be treated equally, she said.

She called for a constitutional amendment, of federal laws, to end discrimination. Otherwise “we won’t have anything change”. The speech earned whoops from the media room.

The speech was immediately praised on social media, though some predicted that it could earn Arquette a rightwing backlash.

can't quite articulate how much that Patricia Arquette speech meant — how effectively & concisely you can use that platform for awareness — Anne Helen Petersen (@annehelen) February 23, 2015

It was the second feminist moment of the night, after Reece Witherspoon used Instagram to promote #AskHerMore, designed to encourage the media to ask female actors on the red carpet weighter questions than the hardy perennial: “Who are you wearing?”