House speaker John Boehner has admonished a senior Republican colleague over the use of a racial slur to describe Hispanic immigrants.

Boehner joined other Republicans in demanding a full apology of Alaska representative Don Young, who drew widespread condemnation for calling Hispanics "wetbacks" in a radio interview.

Young, who has represented Alaska's at-large district in the House since 1973, said he meant "no disrespect" by the comment.

Boehner described Young's remarks as "offensive and beneath the dignity of the office he holds". He added: "I don't care why he said it; there's no excuse and it warrants an immediate apology."

The Democrat minority leader of the House, Nancy Pelosi, also called for a full apology over the "deeply offensive" remarks.

The phrase "wetback" is regarded as an offensive slur. It was originally used to describe Mexican immigrants who entered the US by crossing the Rio Grande.

Young, speaking on KRBD radio, was discussing how the mechanisation of farming practices had led to fewer jobs. He said: "My father had a ranch – we used to have 50 to 60 wetbacks to pick tomatoes. It takes two people to pick the same tomatoes now. It's all done by machine."

In a statement released on Thursday, Young said he had used the term innocently, and meant no harm by it.

Young, 79, said the phrase was one he "commonly used during my days growing up on a farm in central California". But he accepted that the term was "not used in the same way nowadays and I meant no disrespect".

But in a tweet, Pelosi dismissed Young's apparent defence that the term has become more offensive with time.

"Congressman Young should fully apologise for deeply offensive comments that were not appropriate in his youth or now," she said.

Young's comments come at a sensitive time for the Republicans, with many in the party looking to soften its line on immigration following November's election loss.

A record number of Hispanics voted, making up 10% of the overall electorate, according to the Pew Research Center. Of those, 71% favoured Barack Obama over Republican rival Mitt Romney.

American Crossroads – the conservative Super Pac backed by former George W Bush adviser Karl Rove – recently launched a fighting fund to counter "undisciplined" primary candidates from the fringe of the party.

It comes after a brace of high-profile Senate seat defeats in November where Republican faced a backlash over comments on rape and abortion.

Meanwhile, a Michigan member of the Republican National Committee (RNC) was under increasing pressure on Friday to resign over an anti-gay diatribe posted on Facebook.

Dave Agema, who served as a state congressman from 2007 until late last year, put up an excerpt of an article titled Everyone Should Know These Statistics On Homosexuals.

Among other homophobic slurs, the article describes homosexuality as a "filthy lifestyle", adding that gay and lesbian people have an agenda of turning people against Christianity.

It also claims that many gay people admit to being paedophiles.

A group of 21 Michigan Republicans have since called the paper "deplorable". Agema also appeared to receive a rebuke from RNC chairman Reince Priebus.

Priebus said that although the party's position on gay marriage – an issue that this week went before the supreme court – is clear, "all human beings deserve to be treated with dignity and respect."

Despite increasing pressure over the article posted on his Facebook page, Agema told the Associated Press that he will "absolutely not" resign from the RNC.