Donald Trump’s nominee for US attorney general will be forced later on Tuesday to defend a career dogged by claims of racism and bigotry, as Democrats begin a struggle to block cabinet appointments made by the president-elect.

Jeff Sessions, a law-and-order Alabama conservative loathed by civil rights activists, is due to be questioned by senators at the first confirmation hearing of an overloaded week in Washington, where Republicans are moving to steamroller opposition to nine of Trump’s contentious selections.

Democratic Senate leaders have accused Trump of trying to “jam through unvetted nominees”, while in an extraordinary statement, the nonpartisan Office of Government Ethics condemned the “vote-a-rama” strategy as unprecedented in its four-decade existence.

The Senate majority leader, Mitch McConnell, dismissed such concerns on Monday. “Everybody will be properly vetted as they have been in the past,” he told reporters after meeting Trump in New York, “and I’m hopeful that we’ll get up to six or seven – particularly the national security team – in place on day one.”

The selection of Sessions, who was denied a federal judgeship 30 years ago amid explosive allegations of racial discrimination, has met especially strong opposition from campaigners distressed by the senator’s record on a wide range of issues.

David Cole, legal director of the American Civil Liberties Union (ACLU), is to testify at the Senate judiciary committee hearing despite the group’s longstanding policy of remaining neutral on presidential appointments. Letters of opposition have been sent to senators from campaigners for the rights of women, LGBT people, racial minorities and many others.

Jeff Sessions has been accused of ‘disregard for the rule of law and hostility to the protection of civil rights’. Photograph: Jonathan Ernst/Reuters

Writing on behalf of 200 campaign groups, the Leadership Conference on Human Rights said: “Senator Sessions has a 30-year record of racial insensitivity, bias against immigrants, disregard for the rule of law and hostility to the protection of civil rights that makes him unfit to serve as the attorney general of the United States.”

Sessions, who has also come under criticism for his hardline anti-immigration stance, has vehemently denied being racist. His nomination has attracted support from several law enforcement and police groups in addition to conservative campaigners.

The Senate must vote to approve a president’s major appointments. As the minority, Democrats will be unable to block any of Trump’s picks who receive full Republican support. Sessions, who has cultivated deep relationships with colleagues during 20 years in the upper chamber, is likely to be approved.

Speaking to reporters at Trump Tower in New York on Monday, the president-elect said he was not concerned about Sessions’ chances, calling him a “high-quality man”.

“Confirmation is going great,” Trump said. “I think they’ll all pass … they’re all at the highest level.”

Rex Tillerson, Trump’s nominee for secretary of state, appears most in danger of facing dissent from Republican ranks over a close relationship he has built during his work as chief executive of the Exxon oil corporation with Vladimir Putin, the Russian president.

John McCain, the hawkish Arizona senator and former presidential candidate, has said that while he may support Tillerson’s nomination, “there’s also a realistic scenario that pigs fly”.

Tillerson’s confirmation hearings are scheduled to begin on Wednesday, when they may be conveniently overshadowed by Trump’s first press conference since July. Also planned for Wednesday are confirmation hearings on Trump’s nominees for CIA director, education secretary and transportation secretary, and a second day of hearings on Sessions, in which black congressmen are expected to testify against him.

In 1986, Sessions became only the second person in 50 years to have his appointment to a federal judgeship denied by the Senate, after Democrats such as Joe Biden and Ted Kennedy voted against his nomination by Ronald Reagan.

J Gerald Hebert, a former justice department civil rights attorney who worked with Sessions in Alabama, testified to senators that Sessions had dismissed organisations such as the National Association for the Advancement of Colored People (NAACP) and the ACLU as “un-American” and suggested a white civil rights attorney was a race traitor for taking on a voting rights case in Alabama during the 1980s.

Senators also heard that Sessions had referred to a black official in his US attorney’s office as “boy” and instructed him to be careful what he said to white people. If confirmed, Sessions would succeed the first and second black US attorney generals – Eric Holder and Loretta Lynch.

More recently, Sessions has courted controversy by sharply attacking the Black Lives Matter protest movement, which he called “really radical” and blamed for a spike in violent crime in some US cities.

In an interview with the Guardian, Hebert said Sessions had “never apologised” for the offensive remarks aired in the 1980s and since then “really hasn’t done anything to forge a record of fairness and equality when it comes to minority citizens”.

He described the prospect of Sessions being America’s most senior law enforcement official as “frightening”.

“I’m concerned not only about his overseeing the civil rights division, which I consider to be the crown jewel of the justice department because it protects fundamental rights of all Americans,” said Hebert, “but also his record for slanting the law.”